Many of those Lappy's have a serious memory bottleneck. Those P4's were designed to run with RAMBUS memory. A 2.4 is running on a 533 FSB--the memory in most lappys will only run 266 at best. That's a bit of a snag right there. Don't worry so much about the CPU speed and spend the extra money on extras--especially memory. A high end P3 with 256/512MB RAM with a fast hard drive on W2K/XP will run about the same as the entry level P4 that's been starved of memory and quality hard drive. At work, I've got a P3 800 lappy with 256MB RAM that runs almost neck and neck with an eMachine 2.4 GHz Celey PC with 256MB DDR (both running W2K). If that PC had been set up with RAMBUS, there would be no comparison. This isn't just conjecture, I've actually benchmarked them with SiSandra out of curiousity.
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.