If he had went Intel he wouldn't even be able to upgrade that far.

(Honestly, a 2 GHz Willamette would be it.)
You do realize there are already 2 mechanically incompatible sockets for the P4, 423 and 478. There are also 2 different FSB speeds (soon to be 3), 400 MHz, 533 MHz, and soon 800 MHz. There is also the question of Northwood support and Hyperthreading support. In the time frame that FOGOLD has had that machine, there have also been two other P3 revisions.
During that time, AMD has had one socket - socket 462. Unfortunately, some of the newer Athlons won't work on "older" boards.
I wouldn't worry about it too much FOGOLD, an 1800 is still plenty fast. Any system you buy today, either Intel or AMD at this point is not going to be that upgradable as far as future CPU support. We got spoiled in the past with the Athlon Tbirds and early XPs. Intel plans to move to a new design P4 later this year (Prescott) which uses a new chipset (Springdale). I believe 3.2 GHz will be the fastest CPU that current i845PE and E7502 (Granite Bay) boards will be able to support. The same goes for AMD, the fastest Athlon XP on the roadmaps is a 3200+ due out in several months. The Athlon 64 is supposed to launch in September, which of course uses a totally different socket than the Athlon XP.