Step 1) make sure the wires are plain, and not crossover....this is to say, if you look at the two plugs, you'll see that the sequense of wires is identical, and NOT reflected.

Step 2) Check IP's and SubNet masks, make sure that are all correct....

Step 3) IF u can connect to you router (Try 192.168.0.1 in IE or which ever browser), check the settings there...

Step 4) If u have used the network cards before, for ADSL or something and u installed software from your ISP then u might need to get rid of some drivers....which is VERY tricky...I simply formated.....

IF you format, make sure every thing is pluged in once u start installing, XP shoud auto-detect the router and possible the Internet connection on it...and will automaticaly set it up for you...no problem....

Hope this helps...I'v had ALOT of headache over network problems in the past.

- Noia

EDIT:

Lol, nebulus200, you posted right before I started typing :P