Vista doesn't have to suck.. I was one of the most avid supporters of XP, and hated Vista with a passion. When I got my new laptop with Vista on it, I decided I'd leave it on and see how it went. I tweaked it until and it ran better than any XP box I have ever had.
The problem with Vista, is it comes with EVERYTHING turned on, which means its really pretty, but its working way to hard just to support itself. I personally like a clean and simple OS without any flashy shiny buttons... or Aero as they call it, so I turned everything off and it looks nearly identical to XP, except the folders are somewhat different. I even went so far to change all the Vista sounds to be XP's.
All in all I am happy with it, had it a year now and haven't reloaded it with XP.
If you get Vista, just turn off the fancy stuff, and it will run great, arguably better then XP. Not worth the 170 for XP.
Most importantly turn off UAC, that's the security agent that ask you 5 times over whether or not you really want to do what you're doing. Although some people leave it on thinking that just because it prompts them to say yes or no and they still say yes every time, that it will somehow protect them better.
Good luck on the choice!