Hi Glenn
Vista SP1 is out in Beta form, (Final release early next year according to Microsoft) and general feedback is that while it tidies a few things up, it does virtually nothing for driver/software support.
Also out in Beta form is XP SP3, (Expected after Vista SP1) and the feedback from this, is that it adds a lot of features that are contained in Vista, but more importantly gives on average a 10% performance boost.
Personally I would stick with XP, (Particularly if you have older hardware/software) and follow the suggestions for hardware in the previous posts.
Hope this helps

Bill