Unable to join Win2k3 Domain from different subnet!?

[CnileSam]

We have been trying to get computers in another doamin from the one the server is on to join the domain, but we have no luck, but the DNS is fine, we can ping the server from the other subnet, just no luck in joining the domain from the other subent? i have searched forumes endlessly and have not found a solution, can onyone out there help us out. We have Windows server 2k3 and the workstation are all 2k.
Any suggestions at all would help. thx.