K8 notsogrand

Hi
I've been surching the internet for a new power supply. And found that
there's every thing from 300w to 1000w and with a wide price range.
I don't know if I should stay with a 500w or can I go smaller like 465w or
go bigger?
I'm not planing to use two video cards or anything.
maybe a second hard drive but nothing that would need 1000w's

My old one was a 500w 20+4 pin.

It will be powering;
K8nha grand with NF3 250Gb chipset
AMD Athlon 64 2.1ghz 3000+
Radeon 512Mb 1600 pro
two sound cards (a sound blaster Audigy 2 and Echo, Darla )
One DVD burner 16X16
two maybe three case fans with LCD lights