My friends half sister has vista on a dell laptop and she says it runs fine but she has 4 gigs of ram. Most people have 2 or 3 I think so how good her PC runs should not really count. But I think it is true that most of Vistas problems are gone.
My father says XP ran really bad when it first came out... but I was too young to remember I think ^^
Uhhhh... I'm on Windows XP Media Center.. uhh... 2002 I believe. Yeah, old. I bought the computer in 2007, and it was a 2005 model... I was looking to go cheap. It's not a bad computer. Came with 1 GB of ram, a 250 GB hard drive... uhh, a really crappy graphics card... and some other stuff I don't know, or care about. When I get a decent amount of money, I'm going to build my own super computer, from the ground up, so I can be 1337. ...
Well, now I wish I could go back and change my answer, because I now use Ubuntu, a distribution of Linux. Its reliable, it actually has a program where all the applications are on there are listed in an organised catalogue. When they're installed, the applications menu on the top lists programs by their category (Games, Office, Graphics, Accessories). I'll post a picture of how it looks after school. Of course, you could just go onto the Wikipedia article and look at it there.
I remember I really liked Ubuntu when I tried it. Its actually lots like Mac OS X. At least I think so. Thats kind of why I liked it. I didn't keep it though... because I like Mac OS X fine and it came on my computer.
But.. if you have windows and want something new... but dont want to pay for a Mac. I think everyone will agree that you should download Ubuntu! ^^