http://support.microsoft.com/kb/928218
follow the link above because yahoo cannot display the complete guide.
--------------------------------------------------------------------------
To uninstall the existing 2007 Office system if you cannot uninstall it by using the Add or Remove Programs feature, follow these steps:
1. Remove any remaining Windows Installer packages of the 2007 Office system. To do this, follow these steps.
Note These steps require that your user account has Administrator permissions on the computer.
a. Click Start, click Run, type installer, and then click OK.
This process opens the %windir%\Installer folder.
b. On the View menu, click Details.
c. On the View menu, click Choose Details.
d. Click to select the Subject check box, type 340 in the Width of selected column (in pixels) box, and then click OK.
Note It may take several minutes for the subjects to appear next to each .msi file.
e. On the View menu, point to Arrange icons by, and then click Subject.
f. For each .msi file whose subject is "Microsoft Office Product_Name 2007," right-click the .msi file, and then click Uninstall.
Note Product_Name is a placeholder for the name of the 2007 Office product.
2. Stop the Office Source Engine service. To do this, follow these steps:
a. Click Start, click Run, type services.msc, and then click OK.
b. In the Services window, determine whether the Office Source Engine service is running. If this service is running, right-click Office Source Engine, and then click Stop.
c. Close the Services window.
3. Remove any remaining 2007 Office installation files and folders. To do this, follow these steps:
a. Click Start, click Run, type %CommonProgramFiles%\Microsoft Shared, and then click OK.
b. If the following folders are present, delete them:
• Office12
• Source Engine
c. Click Start, click Run, type %ProgramFiles%\Microsoft Office, and then click OK.
Note On a computer that is running a 64-bit version of Windows XP, type %ProgramFiles(x86)%\Microsoft Office instead.
d. Delete the Office12 folder.
e. On the root folder of each hard disk drive, locate and then open the MSOCache folder. If you cannot see the MSOCache folder, follow these steps:
1. Open Windows Explorer, and then click Folder Options on the Tools menu.
2. Click the View tab.
3. In the Advanced settings pane, click Show hidden files and folders under Hidden files and folders.
4. Click to clear the Hide protected operating system files check box, and then click OK.
f. Open the drive_letter:\MSOCache\All Users folder, and then delete every folder that has the following text in the folder name:
0FF1CE)-
Note This text contains a zero and a one for the letters "O" and "I."
g. Click Start, click Run, type %appdata%\microsoft\templates, and then click OK.
h. Delete the following files:
• Normal.dotm
• Normalemail.dotm
i. Click Start, click Run, type %appdata%\microsoft\document building blocks\Language_ID, and then click OK.
Notes
• If you cannot open this folder because the folder does not exist, go to step 3k.
• Language_ID is a placeholder for the four-digit number that represents the language of the 2007 Office system. For example, if you use the English version of the 2007 Office system, the Language_ID value is 1033.
j. Delete the Building blocks.dotx file.
k. Click Start, click Run, type %temp%, and then click OK.
l. On the Edit menu, click Select All.
m. On the File menu, click Delete.
n. Click Start, click Run, type %AllUsersprofile%\Application Data\Microsoft\Office\Data, and then click OK.
o. Delete the opa12.dat file.
4. Remove the registry subkeys of the 2007 Office system. To do this, follow these steps.
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
a. Locate and then delete the registry subkeys of the 2007 Office system if they are present. To do this, follow these steps:
1. Click Start, click Run, type regedit, and then click OK.
2. Click the following subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0
3. On the File menu, click Export, type DeletedKey01, and then click Save.
4. On the Edit menu, click Delete, and then click Yes to confirm the deletion.
5. For each registry subkey in the following list, repeat steps 4a(1) through 4a(4). Change the name of the exported key by one for each subkey.
For example, type DeletedKey02 for the second key, type DeletedKey03 for the third key, and so on.
Note In the following registry keys, the asterisk character (*) represents one or more characters in the subkey name.
• HKEY_CURRENT_USER\Software\Microsoft\Office\12.0
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\12.0
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Delivery\SourceEngine\Downloads\*0FF1CE}-*
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*0FF1CE*
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UpgradeCodes\*F01FEC
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\*F01FEC
• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ose
• HKEY_CLASSES_ROOT\Installer\Features\*F01FEC
• HKEY_CLASSES_ROOT\Installer\Products\*F01FEC
• HKEY_CLASSES_ROOT\Installer\UpgradeCodes\*F01FEC
• HKEY_CLASSES_ROOT\Installer\Win32Assemblies\*Office12*
Note If the computer is running a 64-bit version of Microsoft Windows, locate and then delete the following subkeys:
• HKEY_CURRENT_USER\Software\Microsoft\Office\12.0
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\12.0
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\Delivery\SourceEngine\Downloads\*0FF1CE}-*
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*0FF1CE*
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Installer\UpgradeCodes\*F01FEC
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\*F01FEC
• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ose
• HKEY_CLASSES_ROOT\Installer\Features\*F01FEC
• HKEY_CLASSES_ROOT\Installer\Products\*F01FEC
• HKEY_CLASSES_ROOT\Installer\UpgradeCodes\*F01FEC
• HKEY_CLASSES_ROOT\Installer\Win32Assemblies\*Office12*
b. Locate the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
Note On a computer that is running a 64-bit version of Windows, locate the following registry subkey instead:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall
c. On the File menu, click Export, type UninstallKey01, and then click Save.
d. Under the Uninstall subkey that you located in step 4b, click each subkey, and then determine whether the subkey has the following value assigned to it:
• Name: UninstallString
• Data: file_name path\Office Setup Controller\Setup.exe path
Note In this example, file_name is a placeholder for the name of an installation program, and path is a placeholder for the file path.
e. If the subkey contains the name and the data that are described in step 4d, click Delete on the Edit menu. Otherwise, go to step 4f.
f. Repeat steps 4d and 4e until you locate and then delete every subkey that matches the name and the data that are described in step 4d.
g. Close Registry Editor.