Go through the "My Documents" folder and delete anything you don't need. Then, go to the control panel and Add/Remove Programs via:
Start > Control Panel > Add/Remove Programs
use that utility to uninstall any program or application that you don't or won't use. After that, you can go to:
Start > All Programs > Accessories > System Tools > Disk Cleanup
It will run a scan for you and tell you about anything that coul be taking up extra hard drive space and slowing you down. Run whatever you are willing to, but you should be safe with every option because you'll mostly be turning off Windows features that you don't use.
Next, go to http://www.ccleaner.com/ download and install Ccleaner. After you are finished installing it, run the cleaner on default setting. After the cleaner completes it's work, go to the Registry tab. Tell it to fix all registry problems and make a backup of your registry, if anything goes wrong after the fix you can reinstate your old registry to fix it.
After all of that go to:
Start > All Programs > Accessories > System Tools > Disk Defragmenter
Run the defrag which, depending on the size and speed of your hard drive will take between 30 minutes to 3 hours.
After all of that your computer will be ready for a reboot and should run much more smoothly and quickly.
If you still need more send me an email.