That is generally the best idea. There is so much junk and useless crap on pre-built comps its not even funny. If I were you as soon as I got it out of the box I would get all the drivers and crap ready and just format and re-install. That is the best idea. You could try regedit or msconfig to check to see what programs are starting up when the computer boots but I promise you it will be very confusing since you didnt install any of the crap and its all in foreign directory locations and generally a big hassle. Also; if you format it and reinstall XP, enable the built-in XP firewall (unless you have a router) since it isnt enabled by default.
Dude, one big problem is it's a Dell. Not that Dell's are bad, it's the fact that the preloaded software makes beautiful Dell PCs run like freaking 10 year old emachines. Format it, reinstall XP, and get a nice video card.
still bashing Intel, you do know that in the benchmarks P4's performed better than AMD Athlon XP's (in fair tests, 2.5GHZ verses 2500+ and same spec PC's); they are more expensive, but not by much now.
now with the slow problem, I think it has been settled now, format, reinstall everything (including drivers) and if you got Norton with it, ditch it for a fast, and effective antivirus program like AntivirXP or AVG - now I'm not against norton, but I find it is always slow.