Go into bios and make select "boot from cd" or make sure its 1st priority.
No need to alter any bios setting to boot from cd, just press F12 at startup and you should get the one off boot menu list.
Choose cdrom using the up/down arrow keys the press enter and viola, you'll boot from the cd/dvd drive.
Additionally is your xp cd one that includes sp3? If it isn't then to avoid most of the numerous windows updates I suggest you slipstream sp3 to your present version of xp.
As stated before, go to the dell downloads site and get the needed latest drivers after making a note of what hardware you have installed in device manager.