hi everyone...
this is my first system build.. and im having a problem figuring out what psu i should buy...
and how many watts it should have... could u help a rookie out...

well here are the other parts i got for my homebuild system...(hoping it would be a great gaming pc)

AMD Athlon 64X2 dual core processor 5000+

2048 system memory

500gb hard drive

ECS A780GM-A Motherboard - AMD 780G, Socket AM2+, ATX, Audio, Video, HDMI, PCI Express 2.0, Gigabit LAN, USB 2.0, eSATA, RAID

EVGA GeForce 8800 GTS Video Card - 640MB GDDR3, PCI Express, SLI Ready, (Dual Link) Dual DVI, HDTV, Video Card...

if any of you think that i got incompatible things pls tell....(especially the video card and motherboard...not sure if the video card will fit).. and offcourse dont forget to tell what psu would you recommend for me.. for optimal performance with a good price smwer below $120)

im such a newbie at making systems... thats why i nid your expert help guys.... il be w8n for your replies....

and advanced thank you very much....

550-600 watts should probably be enough. Just look for the one with the best reviews and see what the bads ones say. I'd go for a nVidia chipset seeing as your using a nVidia vide/graphics card, my opinion though. ECS, MSI, and ASUS are supposed to be good. I use a MSI myself and it works well and a friend uses a ECS and it works well, so its still a good choice. It all looks pretty good. Make sure you get good quality RAM and not cheap junk if you want good performance. Corsair has good RAM, Kingston and OCZ are good too.