|My upgrade was from a Duron 1300 to a 2400+ Tbred B.|
That sound like an impressive upgrade? I'd guess a perceived performance increase of 20-30% at most. Most of that would have been due to the increased L2 cache and fsb; only a small part to the 700Mhz processor speed increase.
You're not helping out the L2 cache or fsb...only increasing the raw speed by 333Mhz.
I can tell you that increasing memory from 512 to 768Mb will make a big difference running XP. If you do, in fact, need more memory, that would be the area to concentrate on.
Another good point made by jam is the cost of upgrading. 10 bucks would be my limit here too. You can get that much back for your 2000+.