Member Rara Avis
Sorry, by chip set I meant what P4 you intended to plug into it. Doesn't matter, though, because if the computer is only used for Office type stuff, virtually any modern P4 will be more than you really need. With the possible exception of really, really huge and complex spreadsheets, the bottleneck will be the disk drives rather than the CPU.
With XP, you need at least 512M to avoid sluggishness, and a gig would be better. Unless the user is doing something very unusual, anything over a gig of RAM would probably just be wasted. The harder choice is deciding how many SIMMs to use. Fill both slots and it will be more expensive to upgrade later, but using only one slot will be more expensive now. IMO, you will probably never need to upgrade later, but that's obviously going to be a judgment call only you can make.
I would go with DDR400, often designated as PC3200 (named similarly to the almost defunct Rambus memory from a few years ago, with 3200 representing a 3.2 GB/s bandwidth). Your motherboard supports the newer dual-channel DDR400, raising the bandwidth to 6.4 GB/s, but I honestly think that would be a waste of money for simple word processing and spreadsheet applications. Use the money on dual IDE drives, instead, and you'll likely see a much more significant increase in performance.
BTW, I'm really not up on this stuff as much as I was before retiring, so someone with more recent experience might have better advise. I know Ron (C'Pat) and Christopher usually stay abreast of this stuff.