Any documentation about how to hide internal header when routhing from 2007 exchange server to 2003?

situation:  mail is relay to exchange 2003 from exchange 2007 and then delivery to external domain.  But I can see internal ip address of exchange 2007 server while moving message between servers in the header.  This information is carried over to external domain to the recipient.  I guess this is a security concern and need to somehow hide the internal ip address from the header.  Someone suggested try using transport rules on the exchange 2007, but I got stuck when there is something to enter in the remove box.  Would that be local ip address or something else?  What is I want to remove entire transitional header information so it will only show exchange 2003 information upon sending?

Also, my exchange 2003 is presenting as FQDN with .local attached to it.  Where do I change it so that it can be present as .com instead.  Same question for exchange 2007 as well.

Thanks,

Henry