well, i'm no windows networking guru... but here's one possible way to do it without playing with your routing table. comments from those with a clue are welcome...
supposing your existing home network is using 192.168.1.0/255.255.255.0 address range and that your 2 workstations have the netbios name "pinky" and "brain", then...
1) install your new adapters. configure both your new adapters to use the, say, 10.0.1.0/255.255.255.0 address range, using 10.0.1.1 and 10.0.1.2 respectively with a subnet mask of 255.255.255.0 in the advanced ip properties and making sure to leave default gateway field empty (very important).
2) plug in the cable (any standard cat5e cable will do with gigaE, IIRC. i.e. you do not need a "crossover" cable, the adapters are supposed to sort out if you're using straight-through or cross-over cable using MDI-X,
http://www.webopedia.com/TERM/M/MDIX.html)
3) ping the other station using its 10.0.1.x address. if it works, you're in business
4) once you get it working, go to the windows\system32\drivers\etc directory on each xp workstation and edit the "hosts" file to add
the following lines
10.0.1.1 pinky
10.0.1.2 brain
If you are using an internal domain, say "home.net", then your lines should look like:
10.0.1.1 pinky.home.net pinky
If you are using Active Directory on your home network, then it's another ballgame.
5) reboot your machines, open a command shell and type on the first machine "ping brain". if you see:
Pinging brain [10.0.1.2] with 32 bytes of data
then your giga link is working.
If it is
Pinging brain [192.168.1.x] with 32 bytes of data
then you may have to look on how the netbios over ip resolver works with windows (lmhosts, hosts, dns, wins, browsing, etc)
HTH