I installed vista, but alot of my previous software and hardware wasn't working so I had to go back to XP. This software does slow down your computer a bit, but not if you have a good computer. The lowest powered I tried this on had specs:
P4 2.4 gHZ processor
768 MB RAM
standard video card which comes with intel processors

and it works flawlessly, even after the third party softwares.

And dlphob, i think you can change the looks of Vista to OSX, I am not sure but I think you can using the OSX transformation pack. What you have to do is right click the setup file of the OSX tranformation pack, click properties and in compatability change it to Windows XP SP2 and it might work. I'm not sure though.