I think THoff is correct, something on your PC (both of them?) has convinced the trial wrapper there is some form of problem.
Personally I would go (2) of Philander's suggestion i.e. reinstall your OS - and have nothing else installed except your OS when you install the trial. f you go this route then you can also almost guarantee that if the VS9 trial doesn't load then it is a bug in the software (perhaps a hardware incompatability????), unless you can guarantee a "clean" base then it could be almost anything causing the problem and nobody is prepared to spend (waste?) too much time trying to work out what might be causing the problem.
I don't pretend to be a Windows registry expert/mechanic or anything like that, I have found from past experience that it is extremely helpful to just periodically blow away the entire disk (after backing up the data!

) and re-installing the OS and all application software. But this is a real pain to do from scratch, so these days I take a snapshot of the (clean) installation using something like Norton Ghost or Image for Windows (later is shareware, so you can try before you buy). Then if I have any doubts of the state of my computer, or want to trial some software that may or may not leave parts of itself behind, I backup my data files, install the trial and then after playtime is over I restore from my (clean) backup discs and have the system in a totally known state - something you can't always guarantee with a Windows computer system.
So perhaps try this:
1. backup your data files,
2. format your hard drive and reinstall your OS
3. take a snapshot of the c: drive using Norton Ghost or Image for Windows
4. try installing VS9 trial and play with it.
5. restore from your backup discs to the c: drive
6. install all your normal application software (Word, Firefox etc)
7. take another image of your c: drive (Norton Ghost or Image for Windows)
8. make a decision whether you are going to buy VS9 or not
If nothing else, this exercise will give you a clean baseline of your system from which to recover at any later stage
Goodluck,
Peter