http://apcmag.com/inside-windows-7s-virtual-xp-mode.htm is the best intro to this software that I can find. I had heard of it, but knew nothing before. Now I know it is a download, you need suitable hardware (but there are few ways to determine if you have it), that you will probably need to pay for it when fully released, that it comes with a ready-built version of XP at some 450Mb, and you will need an XP license. It is for business users anyway and no use for gamers (too slow).
Now to why you cannot unload it.....dont know, but lets guess. (a) it did not fully load successfully (b) the installer is full of bugs (c) the installer currently does not offer an uninstall (d) there is an ominous ring to the words "lets you run a virtual XP session directly inside Windows 7" which could mean it replaces so much Win7 code the only method of removing it is to roll back to before it was installed.
So what can you do ? (a) nothing (b) try install it again which works for some baulky software - Norton springs to mind (c) download it again and hope it is a bit more debugged (d) roll back Win7 to before you installed it (e) delete and reinstall Win7
I dont really understand why MS are developing a virtual
XP package when there is already a virtual
PC package working fairly well in XP and Vista. More of a marketing exercise than a real need I would guess ("oh no, you don't need to waste time installing a copy of XP, just pay the $$$, we will do it for you").
As to the programs you cannot get to work in Win7, you might find virtual PC is a better bet, but I'm not holding my breath.