Please read this ENTIRE posting before actually DOING anything it suggests...
The Office trial that comes on machines today is almost like a virus in its own right. It won't remove easily...
...as you're learning the hard way.
But fear not, it can be done.
You'll need three utilities... only two of which you'll probably end-up using, but it's nice to have the third just in case.
They're all free. Do NOTHING with any of them until and unless you've read and fully understand this ENTIRE posting.
First, download the REVO UNINSTALLER...
http://www.revouninstaller.com/download/revosetup.exe
...and install it. But do nothing with it yet.
Then download the REMOVE OFFICE 2007 utility...
http://www.refusetosuffer.com/downloads/removeoffice2007/RipOutOffice2007.zip
...and then unzip it to some folder somewhere (and please remember where), but DO NOT RUN IT YET... it doesn't need to be installed. Just sit tight.
Then download the WINDOWS INSTALLER CLEANUP UTILITY...
http://download.microsoft.com/download/e/9/d/e9d80355-7ab4-45b8-80e8-983a48d5e1bd/msicuu2.exe
...and go ahead and install it, but DON'T USE IT YET.
Once those three things are done, you are going to first try to uninstall Office using the REVO UNINSTALLER. Revo is nice because it first tries to run the software's native uninstaller (which is what you've also done); but then, even if that fails, REVO will go on and try to hunt down all files, folders and registry entries that are still present. So, then, even if the regular uninstaller fails (which is what you're saying has been happening), REVO will still pretty much get it uninstalled.
Revo will offer four uninstallation methods... you want to use the fourth, most rigorous method. And don't be confused by the fact that Revo's little left-to-right progress bar will be moving even behind the regular uninstaller dialog(s). Just don't let the regular uninstaller screens get "behind" the REVO dialog.
Choose the fourth method in REVO, let it try to launch Office's own uninstaller (which will fail), and then after that, once Revo's progress bar is all the way over to the right and you can click on "Next," do so.
Revo will then hunt for registry entries left behind. It may seem to stall about halfway (or a little more than halfway through... but just be patient). When it finally gives you a list of registry entries left behind, just select them all, and delete them all. Don't worry.... only entries which are in BOLD will actually be deleted, even if all other entries have checkmarks next to them. Then click on "Next" again.
Revo will then look for files and folders left behind. When it finds them, select them all and delete them all. Then click on "Finish."
Then reboot.
When things are back up again, launch the WINDOWS INSTALLER CLEANUP TOOL. Be really careful, because it will rip the guts out of Windows itself and make your machine unbootable.... so slow down and think twice before clicking once with that tool.
Look carefully through the WINDOWS INSTALLER CLEANUP TOOL's list of installed programs. If REVO was successful, you should NOT see Microsoft Office on the list. If Microsoft Office IS on the list, then highlight it on said list (and look twice and make sure it's the right thing that you just clicked-on to highlight) and tell the tool to remove(uninstall) it. A "command" (DOS-style) window or two will pop-up and lots of things will happen; and then you'll be told that it's done.
When it's done, look again, look again on the list and make sure that Microsoft Office is nowhere on it. It will almost certainly not be.
In fact, after REVO, Office will almost certainly NOT be on the list of installed programs as displayed by the WINDOWS INSTALLER CLEANUP TOOL. But I'm having you launch the tool and check, just in case; and if it's there (which it most likely won't be), then go ahead and let the tool try to remove it... which it either will, or it will THINK it did by the time it's done.
Then reboot again.
When the machine's back up, go find the REMOVE OFFICE 2007 utility. It's a simple utility... nothing fancy. Using it involves mostly just left-double-clicking on it to launch it, and then just clicking on "OK" or "Next" or whatever 'til it's done.
Rune the REMOVE OFFICE 2007 utility... and BE PATIENT while it runs. It could take a while. It may even appear to stall. Just be patient. Eventually, however... after like a half hour, if it seems to be just sitting there, then it probably has stalled. But just be patient with it.
Hopefully it will finish and tell you that it has finished. But sometimes it finishes, and seems to just kinda' hand at what, had it finished, would be the second-to-last screen. If that happens, you may have to forcibly close it... and if that happens, even though it may not have finished cleanly, it will likely have actuallyl done its job correctly.
Run it ONLY ONCE unless it really does crash like right after it starts or something... and it's obvious to anyone that it couldn't have gotten anything accomplished in such a short period of time.
Then reboot.
Then, after rebooting, run the REMOVE OFFICE 2007 utility again. And, again, it may or may not finish cleanly.
Then reboot.
At that point, Office 2007 should really and truly be off your machine. Sadly, some registry entries may still be left behind, but they will be inconsequential.
Some folders may be left behind, too (even REVO was supposed to have removed them). If so, they won't really be harmful in any way.
If you know how to manually hunt down leftover registry entries and files/folders you can do it, but I wouldn't worry about it. The salient core of Office -- the part of it that makes Windows think it's installed -- will have been removed.
At that point, you can install a full version of Office if you like; or Open Office, or whatever you have in mind.
Sadly, there are two registry entries that sometimes get left behind which will fool the Windows updater into believing that Office 2007 is still on the machine; and you may be offered an Office 2007 update or patch every now and then. If so, just shake your head in disbelief and let them install. They're harmless... won't hurt a thing.
Once it's all overwith, you can delete the REMOVE OFFICE 2007 utility off your machine.
However, both of the other utilities may come in hand someday. The Windows installer screws-up all the time; you may need the cleanup utility. Just remember that it's VERY potent. Don't accidentally remove the wrong thing with it.
And REVO UNINSTALLER should become the ONLY uninstaller you ever use; and its fourth and most rigorous medthod should be the only one you ever select. REVO is, by far, the best of the free deep uninstallers out there; and it should be used by you, from now on, instead of Add/Remove Programs...
...that is, unless your goal is to repair an installation (as can sometimes be done from within Add/Remove Programs, and can't usually be done from within Revo). So you may, occasionally, still go into Control Panel and use Add/Remove Programs, but, again, only to repair, never to uninstall. To uninstall, from now on, ALWAYS use Revo. It's just superior.
Hope that helps. Good luck.