Trying to get PerX to work for Vista is a sticky sutiation no doubt.
You said you changed the compablilty for vista, when most people change it to "Windows Xp (Service Pack 2)"
But If you click start and right click computer go to properties, and your computer information comes up, its bound to say something else, like mine says...
[IMG]http://i344.photobucke*****m/albums/p329/KiddKarma/SP1.jpg[/IMG]
You could try changing it to whatever it says here, but also try Windows XP (Service Pack 2).
Mods might wanna look into making this a sticky for the Choobs in need out there.

But than again most people already know how to use it.
Very Imformative Tutorail on using PerX:
1. Run as Admin ALWAYS a must.
2.Load you .dll file using the Browser button.
[IMG]http://i344.photobucke*****m/albums/p329/KiddKarma/2.jpg[/IMG]
3.Type in "crossfire.exe" into the "What to inject:" box. Processes are case senseative.
[IMG]http://i344.photobucke*****m/albums/p329/KiddKarma/3.jpg[/IMG]
4.Tick the box/circle that says "Automatically" to ensure that the .dll is injected the easy way.

(We all love easy now don't we.)
[IMG]http://i344.photobucke*****m/albums/p329/KiddKarma/4.jpg[/IMG]
5. After all this your set, and you load the game normally, when you hit Start Crossfire, at the bottom of the .dll it will run through a couple different sentences.
[IMG]http://i344.photobucke*****m/albums/p329/KiddKarma/Processes.jpg[/IMG]
6. After this Crossfire should load and you activate your hacks in game.
Slightly harder way to do it.
1.Follow all the same steps. 1-4. From the other guide.
2. Instead of ticking the box/circle for "Automatically" this time. Check the box for "Manually" and "Quit when finished".
3. After loading up the game launcher.
4. Quickly hit start game than hit the inject button on PerX.
Any questions don't be afraid to pm me. ^^
Karma.~