Security patches and driver support is why XP.
IMO it makes no sense to run anything other than a stripped down XP. Its essentially the same as W2K but far more stable than 98 and earlier verions. It runs as fast if not faster than W2K and 98se. But the BIG thing with XP is vastly better driver support, AND Windows update to get the latest patches and fixes for security.
I've run it on machines with 192MB RAM and 400mhz CPU's. For general office stuff its fine. You just have to turn off all the crud and services you don't need.
Learning to do this is a very good thing to learn. As you should be aware services you are running and thus be aware when something unsual starts running in there. You shoud do the same on computer even if its very latest and fastest one.
Or go with Linux, but thats a whole different learning curve.