i recomend a fresh clean windows XP install... in a new partition(maybe in another higher capacity disk?) so that you can have a windows for maya and another for other things on the same computer...)

When you install programs they mess with the registry and make you slow (the more programs intalled the slowest the pc... sad but true)

The graphics card is pretty the most impotant thing for working with maya (when you render you dont care 3 seconds more for a frame because you have a 1500 mhz instead of a 2000mhz... but when you are working with the model it sucks working at 1fps...)

On a fresh XP install you should be fine on realtime if you dont use ultra-hi poly scenes... (200000+ or so, then you should notice slowdowns...)
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Grrr,(envy)DVDrewritable....