I used to have to reinstall windows every 6 months when I had that piece of crap Microsoft released called millennium edition.
I have to concur with the majority, a good old format C does wonders.
It is not hard, it is not really troublesome, XP carries most drivers and those it doesn't can be detected by XP and downloaded direct. Very few drivers would need installing again from CD's.
For programs that's a different story, obviously everything you use as third party software would need to be reinstalled.
I have a HD caddy with about 3 drives in it, I back everything up to that before doing a reformat.
But you should always remember to keep any saved files from any application off your C drive anyway so you never lose anything in a reformat, saves a lot of worry if it ever needs to be done.