I also run an XPS M1330 with Vista, great laptop by the way - best purchase I've made!
But I run AVG free on my work machine, that runs Vista, no problems at all.
I have open office on my XPS, and there have been no problems with that either!
Vista itself hasn't been a major problem on the XPS, just the UAC which can get annoying when you are tweaking the system itself.
Enjoy!