To be equivalent, you could pick up an AMD Athlon XP 2400+, but why would you want to do that? Personally I would never buy a new computer to get exactly what I already have...not taking the opportunity to upgrade is a waste of money. Personally, I'd settle for nothing less than an AMD Athlon 64 3200+ (socket 939). That will give you a big performance upgrade, plus set you up for the future with a 64-bit processor. Then, for true power, look into AMD's X2 or FX-57 processors...wave hello to the future and goodbye to that stack of gold in your basement at the same time.
As far as AMD in general, they're really good. I was with Intel up until December, when I picked up an HP with an AMD Athlon 64 3300+. I'm not sure if I'll ever go back, knowing that my AMD runs cooler, offers better production, is more easilly overclocked, and costs less than its Intel equivalent. I'm planning on building my own computer here shortly, and an Intel processor hasn't even crossed my mind.
Hope this helps,