I've heard so many bad things about Vista but in my personal experience, the bad rap isn't deserved and I'm not sure I even want to try Win 7 for a year or two.
I recently bought the wife a new PC with Vista home premium 64. It's very fast and smooth. Hasn't crashed once. She likes the way it looks too.
She's not a power user and didn't have any problems figuring out how to get the things she does done. Playing games, burning CD/DVDs, email, using open office etc.
The desktop is pretty standard these days. Pentium dual core 2.5g processor, 6 gig of RAM, and a 640G hard drive.