Well, it seems that the new power supply unit really cooks things up.
I have been running WinXP Smoothly without any problem since...about the last 5 hours.
I'm gonna recommend at least 425Watt for the latest pc and graphic cards.
In my case:
Pentium 4, 3.06Ghz.
ATI All-In-Wonder Radeon 8500, 128MB VRAM (I think this is power hungry)
Now I can start whatever projects I have been working on...quick.