In theory, you could do it, but I don't recommend it. E2K7 is 64-bit, and all the OCS components are meant for 32-bit OS. But you could probably get it to work on the 64-bit.
If you do that, you'll need to allocate a new IP address on the CAS for CWA. And yes, you can use ISA 2006 to publish CWA.
However, I would really recommend just putting CWA on a different box - like an existing web server running IIS on 32-bit Windows Server.
Regards,
Matt