WinXP & Samsung NIC - help!

I'm very new to all this networking business, but I have 2 PCs - an ancient
P133 running Windows 95 and a 1.4GHz running Windows XP. I have a 3-Com
3C515-TX ISA network card in the Win95 PC (drivers installed correctly) and
a Samsung SC-1200TX PCI NIC in the WinXP PC (salvaged from an unrelated
computer a couple of years ago). However, Samsung's driver download centre
seems not to know about this particular card (in fact it knows nothing about
any Samsung NICs), and WinXP recognises it as "Intel 21140-Based PCI Fast
Ethernet Adapter (Generic) #2".

I installed all the necessary OS networking bits on each PC, set one up with
an IP address of 192.168.1.1 and another with an IP address of 192.168.1.5.
I set up a new user account on WinXP for the Win95 PC to log on to. I did
all I thought was necessary.

Now here comes the interesting bit. Before I got the ISA card for the Win95
PC, I had already installed the Samsung PCI card in the WinXP PC, and to
stop it getting confused and telling me that 'a network cable is unplugged',
I disabled the card in the Device Manager. Some months later, having
installed the ISA card in the Win95 PC, then installed the drivers for it,
and still with the WinXP card disabled, I connected the crossover cable and
turned on both PCs. The 'link' lights on both cards lit and stayed lit. But
then, enabling the Samsung card in WinXP's device manager leads to the
'link' lights going out, and never coming back on again, no matter how many
times I switch off and restart both PCs, and disconnect and reconnect the
crossover cable (Cat 5e).

Has anyone come across this before? It may be a fault with the Samsung
network card itself I guess (there's a new one of a different make on its
way just to make sure), but I'd like to know whether there's a reason for
this!

--
Ed Fielden