Here's Intel's compatability page for this mb:http://www.intel.com/support/motherboar ... 020076.htm
According to them, you can use up to a 3.06GHz cpu at 533 FSB if your BIOS is up to date. Looks like you can pick these CPUs up on ebay for $15 or so if you re-use your existing heatsink and fan. Be sure you get the mPGA478 version, as that's what your socket is, and there are other P4 3.06 chips with different sockets.
This'll give you a fair bit of improvement over your 2.4GHz cpu for a small price, especially if your old FSB was 400MHz, but it won't be magic. Your hard drive interface and memory bus are still older, slower technology.
If you want to keep expenses low, it's hard to go wrong with this approach. Likewise, if your CPU speed limited you before, this will buy some breathing room. Much more of an upgrade would require new memory, MB, cpu, and possibly power supply.