Network Cards Fighting

Ok here is my situation as a week ago. I had a standard 10 Megabit network with BNC Cable between 3 machines and sometimes up to 10 if I have visitors over. (Now myself I only have 3 so I wil concentrate on those.) I have 2 Athlons that I use for main work running Windows XP Pro SP1. Now I wanted 100 Megabit JUST between those 2 machines because I am usualy transferring a lot of files between them with microsoft filesharing and I wanted the standard 10 megabit BNC left in place without dirturbing it for the lan parties. Ok I got mysef a couple on intel 100 pro network cards and a crossover cable and plugged them in. Now all microsoft networking between these 2 machines stopped. They could ping each other over the 100MBps network cards though not the 10MBps. Fine I decided to start from scratch. I set the 2 machines up like this. Machine 1: 10MBps Card IP address 192.168.0.123 Subnet 255.255.255.0 (have also tried 255.255.0.0 but no diference) 100MBps Card IP Address 192.168.0.133 subnet 255.255.255.0. Machine 2: 10Mbps Card IP address 192.168.0.124 subnet 255.255.255.0 100MBps Card IP address 192.168.0.134 subnet 255.255.255.0. Now I did get it working after a while with these settings but scanning the network to try and connect to each other was really really slow. Once they were connected to each other they worked at the full 100MBps but network scaning was still slow. NOTE I did not have access to the 3rd machine to do tests outside of these 2 machines, I tried removing the 10MBps cards from the machines and it works really really fast on everything. Just unplugging the leads from the 10MBps cards make no difference though. Now I am not trying to get a shared bandwidth between the 2 cards thingy going here so dont think that. I AM NOT TRYING TO GET 110MBps. What I want is for the 2 machines to be hooked together by the 100MBps network BUT to also be hooked together by the 10MBps. I dont care if they can see each other on the 10MBps as long as all the other machines can see them and they can see the rest of the network. You follow me? If you dont I will explain again. 3 machines hooked by 10MBps. 3rd needs to see the other 2 and the other 2 needs to see 3. But the other 2 must not be able to see each other across the 10MBps because of the 100MBps link between them. Is that possible? Or is there a proper way of doing this. Any suggestions on how it should be set up would be greatly appreciated. BTW I am NOT using DHCP. All my IP address are manualy set by me because of some of the things I have running on the network it wont work any other way. thanks for any help.
AREA_1