If your printer is directly attached to the network, it doesn't do the usual Windows \\host\printer stuff. Printers such as HP Laserjets with JetDirect fall into this category. Here's how to add such a printer to Windows XP:

1. Open your printer list, hit Add printer.
2. Hit Next.
3. Set to "Local printer…" and uncheck "Automatically detect…". Ignore the fact that it isn't a local printer; Windows is dumb. Hit Next.
4. Select "Create a new port" and set the dropdown to "Standard TCP/IP Port". Hit Next.
5. A new wizard appears. Hit Next.
6. Type the IP address of the printer. The port name will be automatically set. Hit Next.
7. Verify your port settings and hit Finish.
8. Pick the correct driver, e.g. Manufacturer="HP", Printer="HP Color LaserJet 2605dn". Hit Next.
9. Pick a suitable name, like "HP Laserjet - EB2 3224" or whatever. Make it default if you like.
10. Complete the rest of the wizard as normal (Next, Next, Next, Finish).