Are the NIC's in different subnets? Usually, you should use hosts file to tell the client that it can only reach the server through that specific NIC. Also configure the Server Network Interface for the client.

Try to take a look at:
http://softwaresupport.emc.com/support/resolutions/dmfrmresolutionview.asp?id=50319

Of course, this would apply if the second NIC is to abackup network, where the NIC is dedicated to backup purposes. But it should work for most cases anyway.

Any other ideas are welcome.

Why do you run beta 7.3? GA has been out for almost 4 months now. The GA build is 190. Get that sorted first.

nsradmin> print type: NSRLA
                        type: NSRLA;
                        name: hcrvelin;
 NW instance info operations: ;
       NW instance info file: ;
          installed products: NetWorker 7.3.Build.190;
                     version: "EMC NetWorker 7.3.Build.190 ";
                     servers: hcrvelin;
                auth methods: "0.0.0.0/0,nsrauth/oldauth";
               administrator: Administrators,
                              "group=Administrators,host=hcrvelin",
                              "group=Administrators,host=localhost",
                              "isroot,host=hcrvelin";
                 kernel arch: INTEL_PENTIUM;
                machine type: desktop;
                          OS: Windows XP 5.1;
           NetWorker version: 7.3.Build.190;
              client OS type: Windows NT Workstation on Intel;
                        CPUs: 2;
                     MB used: 45615;
                  IP address: 192.168.1.14;