I don't know if the inventory bug can happen in NT SP5 compatibility mode...
Did you try other compatibility options, like disabling desktop composition? Did you try running the game as administrator?
Did you try setting the game resolution and your desktop resolution to be the same? That may help if the problem is in how DirectX is switching resolutions.
To manually uninstall the game you can just delete the Beyond Divinity folder (other than any saved games, which may be in a subfolder; see below), though that doesn't remove a couple registry entries (likely why the auto-run program didn't give the option to install). I've never had a problem re-installing the game, even without properly uninstalling it (ie just deleting the folder to free up some space for something else temporarily), but then I have auto-run disabled, and always just go straight to the setup program on the disk.
Each save is a separate subfolder in the '..\Beyond Divinity\savegames' folder.
Under Vista/7, depending on how the user accounts are set up, if you install the game to the default Program Files path, Windows can create separate savegame folders for each user, and then map that folder to the game's savegame folder (so it will just see the saves for the relevant user).
C:\Users\ %account name% \AppData\Local\VirtualStore\Program Files\Larian Studios\Beyond Divinity\savegames
