Publishing OWA via TMG, during Exchange 2010 and Exchange 2003 coexistence

Hi Guys,

I have one Exchange 2010 CAS and one Exchange 2003 FrontEnd servers. I have configured Ex 2003 FrontEnd server as legacy server and internal redaction works, i.e. both users (Ex 2003 and 2010) use the same URL to access their OWA, and each of them redirected to his appropriate server.

Now I want to publish my CAS to internet via TMG 2010. The OWA of Exchange 2010 successfully published, and Ex 2010 users are able to log in, but Ex 2003 users are not, the redirection doesn't work.

My question is:

How publish both Exchange 2010 and 2003 OWA via TMG? 

Is it possible to publish with the same URL for both users (Ex 2010 and Ex 2003)?