When you reload and XP OS there is an order in which drivers must be reinstall. That order is:

Notebook system software

Chipset

Video

network

Sound

you can find more on this HERE

The first two listed are the most critical as both of these drivers setup the communication between the hardware in the system and the OS so that when the drivers are loaded the OS knows how to communicate with them.

This can be part of your issue

Now it looks like from the Drivers and download page that the hardwar is 3Com

Thanks Dave. 

Does this mean I have to uninstall everything and start over?  :>(

Before you go that drastic I would try booting into Safe mode and installing the system software and chipset, followed by the network drivers.

If that does not work then you may in fact have to to another reinstall of the OS.

By all means follow the (excellent) advice already offered, but it's almost certainly going be re-installing network drivers specifically, which will solve a missing network controller driver problem?

Checking the internal docs for the Inspiron 2500 I show the following drivers are needed for Win2K (the other OS option listed was WinME):

• Intel 815EM Chipset Update
• Intel Video Driver
• Synaptics Touchpad
• SigmaTel Audio Driver
• Intel Speedstep Utility

More than likely the NIC is a 3COM (3C905 variant, most likely) since that was the usual NIC in systems released during that time period.