ISA configuration with Office Communicator Server

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I've brought up an ISA 2006 server for our Office Communicator Server 2007
implementation. I have a DMZ subnet setup that the ISA server is in. The
machine has two network interfaces in it. Both the network interfaces have
an IP address in the same DMZ subnet.
isaexternal - 192.168.1.4/24
isainternal - 192.168.1.5/24 with gateway 192.168.1.1
Both have port 443 open so that I can publish the web components for OCS 2007
I'm having issues getting the ISA server functional. Is there a problem
having an ISA server with two interfaces (internal facing and external
facing) in the same subnet. Should I move one of the interfaces into a
different subnet or can I make the machine work appropriately how it is
configured.
.