Well I'll post my setup for referrence and maybe it will give you an idea. I have a 300w PSU............yes this may seem small, but when you live in CA, and in a house with 3 other comps, the power bill can go through the roof if you have all 4 machines running 8-10 hours a day. Here's my setup, everything runs fine:
P4 1.5ghz @ 1.61 (107 x 15)
768mb PC-133 RAM
1 60gb Samsung HD
1 120gb Maxtor HD
LG CD-RW
ECS P4IBMS mobo
Nvidia TNT2 (120/125) @ 150/155
3 80mm case fans
1 40mm fan for the TNT2
Intel Stock CPU fan
12" Cold Cathode
All of this H/W runs fine........the CPU voltage is 1.68v, I have a fanbus, but it is only on/off. Yes 350w+ PSU's are nice, but you dont always need em.