you should only need one network card...
So, is the xp computer working as it should be?
I can't say I know anything about WinME so i can't rele help in this area.
As you have one corking computer (I think) use your internet brouser to access your routers settings page [this is usualy hone by typing in
http://routersIP].
Somewhere in here there should be the option to dissable the DHCP feature (i dont know where, it varies from router to router)
For WinXP, you need to go into the control panel and access network connections.
Under here, find your network card and type in your desired IP address (e.g. 192.168.1.2 with subnet:255.255.255.0). Make sure the DNS is setup to that of your routers IP.
Make sure that the computer is setup for a specific workgroup (click on setup network [i think on the panel on the left of the window]). NB you will probably have ot reeboot.
Once back up, check the connectivity to the router and the other computer by:
1) Click start and run
2) run "CMD"
3) in here, type "ping [routers IP]" (this will tell you if there is any communication accross the network)
if this works on both computers, then try pinging from one computer to another
There could be other factors causing problems... tell me how you get on