Ultimately your PXE clients need to be told where to find WDS1 as WDS2 is still responding to their requests.
The PXE client will acquire an address from a DHCP server and then locate the PXE server, both of which are performed using UDP broadcasts. If the two servers are separated by a router (or on different segments) then the broadcasts won't be reaching WDS1, so I am assuming that your two WDS servers are on different network segments.
That I know of, there are two possibilities for configuring which server the clients use for deployment: using DHCP options and using IP helper addresses.
- DHCP options 66 and 67 can be configured to direct the client to the correct server.
- IP helper addresses are used to forward UDP broadcasts onto an address on a different network segment.
See the following article from the Microsoft KB which explains the difference between the two in quite some detail: http://support.microsoft.com/kb/926172
This one should also help you on your way: Managing Network Boot Programs (Microsoft TechNet)
Which option is better for you could probably be answered with a bit more detail about the network infrastructure that lies under your two organisations and their WDS servers, for example what address ranges are being used, routing mechanisms in place, how many DHCP servers and where they are placed, operating system versions, etc.