Ruf

I am planning on setting this up in my house, and I realize that it is a little bit rigged, but I'm trying to achieve this with little to no cost, since I have PSU's, an amp and a sub. I just wanted to get everything straight considering the watts before I go hacking and soldering.

I've recently caught bass fever and now my home setup just won't due. This being said I have a spare 600 watt amp and was planning to hook up a sub on my home system. I looked into modifying a computer psu to power the car amp over other solutions simply because I build computers as well and have a few laying around. The only thing I'm unsure of is this... am I going to need a power supply over 600 watts to power the amp? I don't plan on maxing it out but even if I were to I wasn't sure if I just needed any old 12 volt rail considering thats all a car battery is.