Uninstall/reinstall problems

[Ode to a Grasshopper]

Hey all, I've been doing a canon run with a Unfinished Business, Kivan, Xan, Saerileth, Dungeon-Be-Gone, Level 1 NPCs, and the G3 Tweak and Fixpacks. Something in the Tweakpack was stopping me from enetering the Thieves Guild room to see Renal Bloodscalp. This is the second time this has happened since installing UB; the last time I did a total reinstall and it fixed the problem, so I tried it again - uninstalled everything but the official games, uninstalled ToB, and tried to uninstall SoA. Trouble is, it won't let me uninstall SoA for the full reinstall, and when I tried reinstalling ToB after deleting and then returning the SoA C folder it says the registry can't be found. When I put in the SoA disc it starts with the play option, but when I try to play it has the missing registry message.
In short, I'm sunk - does anyone know how I can uninstall it properly so I can do the full reinstall again? This really sucks.

[Thrar]

The easiest way to install the game is probably to just start the installer directly instead of through the startup screen. Check what you can find in the root folder of CD1, there's probably a setup.exe, install.exe or something like that. Just start it directly and you're probably fine.

Alternatively you could manually delete all registry entries ("keys") related to BG, then it should properly treat it as "not installed". To do that, go to Start->Run and enter "regedit". Make a backup (there's a menu item for that) of the registry first, save it somewhere on the disk.
Use the search function to look for "Bioware" and "Black Isle" (I'm not sure which one, both might exist) and delete the whole folders. If you have any other software by these companies, only delete the subfolders related to BG.
There are probably several such folders, delete them all until the search returns no more results. Since I don't know the exact names or locations of these folders, if it's not sufficient, try searching for some other related words, e.g. "baldur". Most software uses their company name as folder name though.

Make sure you don't delete anything else or you may be in for nasty surprises. The registry is at the heart of the Windows configuration, don't mess with it unless you know what you're doing. If my first suggestion works, preferably keep your hands off the registry entirely.
Make sure you make that backup first if you edit the registry, if later you find out anything is broken, you can revert to it.

[Crenshinibon]

While it's something similar to what Thrar suggested, try an application called "[url="http://www.revouninstaller.com/revo_uninstaller_free_download.html"]Revo Uninstaller[/url]". It essentially walks you through the process of complete uninstallation, but finds all of the files associated with the original installation as well as the registry keys, so you don't have to look for them yourself.

This is a much safer alternative to the above suggestion. No one should ever go into the registry unless they know their way around.

[Ode to a Grasshopper]

Cheers guys, tried the uninstaller but obviously didn't delete enough files, so just ran the install file from the disc and so far it's reinstalling.
Fingers crossed.

EDIT - reinstalled OK, but UB still won't let me do the Thieves' Guild quest. Might just leave it a while until the next update comes out.
Cheers again for the suggestions.