How much power supply do I really need??

I would forget about getting the older PSU repaired and just buy a good quality 500-650 watt PSU.This will enable you to purchase a faster,more power hungry GPU as well as upgrade your CPU.Not to mention adding another HD if you want.Repairing old PSU is a waste of time unless it is some odd ball thing that is required for the system itself.Even then,I would just replace it.Goodluck.

Dahak

M2N32-SLI DELUXE WE
X2 5600+ (3.2)
4X1GIG DDR2 800 IN DC MODE
TOUGHPOWER 850WATT PSU
EVGA GTX 260
SMILIDON RAIDMAX GAMING CASE
ACER 22IN WS LCD 1680X1050
250GIG HD/500GIG HD
G5 GAMING MOUSE
LOGITECH Z-5500 5.1 SURROUND SYSTEM
500WATS CONTINUOUS,1000 PEAK
WIN XP MCE SP2

I agree that a 300 watt power supply is all that's needed.
However, getting a decent quality power supply is going to cost you at least $50. Anything less will be prone to early failure and jeopardizes other parts.
Now, you may ask, what can I get for $50? Looking at Newegg.com:
PC Power & Cooling Silencer 500 PPCS500D (After rebate and free shipping)
Antec Earthwatts EA500
FSP AX500-PN
Seasonic S12 II SS-330.
All the above cost about the same in the end and any will work just fine for your system.

Antec Earthwatts:

http://www.newegg.com/Product/Prod [...] earthwatts

Newegg has the 500W model for $50 and the 380W model for $40.