back when I did SETI, it took about 4.5 hours to do a work unit at 1.4 ghz (3.0.3)
What client are you using?
If you're using the graphical client, I highly recommend getting the command-line client because there is absolutely NO use for the pretty colors that the graphical client draws.
You should be able to do those work units in 5-6 hours with that T-bird 1.2