Ok, read this forum first, a lot of good info.... When you first get it check it out to make sure its ok, then plug it in and turn it on. Look at the screen for any probs check the system specs to make sure you got what you paid for. Run a DVD to check for the light prob also make sure to look for any dead pixels.
If you are happy with it get up to date drivers from Dell and then do a clean install of XP, update the drivers then start adding the the things you want.
Add a firewall, virus protection, spybot, Ad Aware, Speedswitchxp, powerstrip, and anything you feel you need.
Check out Blackviper.com and turn off the junk that slows down the machine.
Good Luck and congrats.