I have Vista.
Vista Home Premium, to be exact.
It runs just fine on my 1.2 Ghz dual-core Pentium 4 laptop. 1 Gig of memory, 120 GB hard drive, wireless g card, etc.
I am surprised that it's running fine. Though, there were some XP programs that screwed up IE. It boots far faster than XP does, and I must say that the shutdown process has slowed down. I will be investigating the reason for the slowness in shutting down.
However, I must say that since I tinker with XP often, and now only begun to tinker with Vista, that I've not had many problems...save for my damned portable USB hard drive, which for some reason, cannot get the driver.
Vista says it's a compatibility problem with Texas Instruments flash media device....I have no idea what it is.
I suspect that if I were to install XP on it, it'd run like crazy.