Setting up 4 port server nic

I can not sort this one out.
Single server network. W2K server installed using the onboard nic. I have now got a 4 port server nic and wish to use this to serve three diffrent computer suites in our school. After installing and setting up an array, I am unable to access two of the suites. Connecting the onboard nic to the main switch and all is well, of course.

Any help would be most welcome.

Thanks. Peter