I have a few ~500W PSU's lying around. I am in the process of upgrading to either a Pentium or Athlon Dual-Core (mid-level at best). I will be running 2 HDD's, 2 optical drives, mid-level graphics card or onboard video, TV tuner, SB Live!. What is the minimum PSU specs I should be looking at (i.e- how many amps on each rail)?