Is it for the rig in your sig? or have you built that new computer yet? Any Antec psu will fit. I like the TruePower series. Other than that, Seasonic Super Tornado or Seasonic Super Silencer. If you are feeding the Pentium 3, you dont need more than 300 Watts. If you are feeding more, well, that all depends on what you have. Super Tornado 400 should be enough power unless you have a 2+disk raid array, prescott, and 6800Ultra SLI