The last time I tried doing this, the gain in PPD was not worth the slowdown as far as the science is concerned IMO. Just keep in mind, the P4 with HT is not a true dual core, instead it basically "virtualizes" a second core, so Winderz will still think it is a dual core CPU. Even though Task Manager will say you are only folding at 50%, you are actually folding at 100% (I like to think of this as a flaw in Microsofts programming). By running 2 clients simultaneously, you are essentially only using half the core to run one WU, while the other half is working the other. Depending on which P4 it is, it may be able to just barely make SMP deadlines, as I know ChasR has a few folding SMP. I do believe they are pretty dedicated to be able to make the SMP deadlines.