First, hunt through the entries in Device Manager to make sure that the adapter is really not there. Start > Settings > Control Panel > System > Hardware Tab > Device Manager button. Is anything at all listed under Network Adapters? If an adapter is listed make sure that it is enabled. If one is listed and no error notice is present, the adapter may just need a driver. XP has built in drivers for many adapters, but not all, so you may need to install a driver from the adapter manufacturer, which will be available on the manufacturer's website, or perhaps the Dell website.
If no adapter is listed, go into the computer's BIOS on boot. On your Dell this is probably done by tapping the F2 key, but it may be Delete or another key -- the specific key should be displayed early in the boot process.
Hunt around in the BIOS for an entry for your network adapter. On some computers this would be in Integrated Peripherals, but I have no idea where it is in yours, or even if it is normally present at all. Some Dells have minimal BIOSes. If you find the adapter listed and it is set as disabled, change that to enabled. Hit Escape and choose to save the change to your BIOS, reboot and Windows should notice the adapter.
You can of course screw up your computer by messing with the BIOS. If you get confused about what you have done to the BIOS just shut the computer and let it reboot. If you somehow mess up the BIOS, remove the motherboard battery for 15 minutes and then replace it, and a default BIOS will load when you boot.
Good luck.
NIC is on in Bios.
Thanx.