|You need the correct WinXP disc. If you have the full retail version, that would be best.|
Boot the system, press F2 to enter setup, then check the boot order. Make sure the CD drive is listed before the HDD. Save the settings & exit.
Boot off the XP disc & make sure to "press any key" when prompted. If you don't press a key, the system will bypass the disc & attempt to boot from the HDD.
Once XP setup starts, delete the current partitioning, then recreate new partitions. Format the partitions as NTFS using the full method (not quick), then continue with the installation.
Hopefully you have all the necessary device drivers...chipset, video, sound, network, touchpad, etc. If not, you'll have to go to the Dell site & download them all.