Or, Start Menu>Right click "Computer" :D and then do a little bit of rooting through the stuff there and you'll find the "most important" stuff.
Also, My 1.6 GHz SINGLE-CORE laptop with a 512mb/216mb graphics card could run L4D with good settings. It can run HL:S on full settings with no lag.
So don't worry about newer Pentium 4, because the more important part of the information of single-cores is the L1/L2/L3 cache. I think that newer ones have 1mb L2, so that's fine. The ram, however, is lacking. It's easy to upgrade that, though.