2 network cards connected to 2 routers

i started off with a pc (NT4)on a tcp/ip local network connected to hub is a cisco router for lotus notes and a citrix terminal. the customer then wanted to connect to a second router and run another citrix program not at the same time so after installing a second network card and assigning a gateway to that card as well. i can ping both routers, when i try to run either of the programs i can sometimes connect but most of the time it fails to to get to either server on the other end of the routers when there is one card in a pc there isn't a problem is there a way of making sure the cards only look for there own router.