Dell Dimensions C521 Power Supply Problem

Hi all.
I own a Deimsnions C521 from dell.
AMD AthlonX2 @1.9GHz~1.9GHz
160 gh HDD
512mb x 2 DDR2 Ram
On board Graphics: Nvidia 6150LE
Micro-BTX Motherboard with AM2 socket <-btx motherbaords are a pain
180 W PSU (fried)
Warranty is void

basiclaly what happened was my power supply had a sudden surge from a thunderstorm and gg'd my comp.

given that my comp is of a micro-btx form factor, i want to ask if ATX psu's are compatible?

I am also considering upgrading to an 8800 GT - it requires a 400 W power source. SO is it possible i can install a 400-550 W powersource in my existing Chassis/case? YOu might ahve to do a little research.

What i really want is to replace my defective PSU and add a garphics card in the PCI-E x16 slot. BUt first i need to replace my PSU to turn my computer on.

thanks in advance for all your help..