okay, I'm building a new rig (A64 3000+ , gf 6600GT, dvd-r, 80gb sata, etc.) and I have a fairly good idea about most things, but when it comes to PSU, I know nothing... I mean I know I need at least 400w, and there's a case I'm looking at which comes with PSU (420w), but I read in a couple of places that sometimes the supplied PSU is not enough. So how can I tell? What numbers should I be looking for? since obviously the 420w doesn't mean much...?