Hi,
Just checking, have you migrated the Email address policy over to Exchange 2007? If so then yes it won't as you say create the GWISE addresses.
I worked on a GW to E2k7 migration and ran into exactly this problem. In the end I left the policies to be managed by the RUS on the e2k3 staging server.
Is that viable for you?
Cheers
Nathan
Nathan Winters - MVP Exchange Server
MCSE & MCSA 2000 & 2003 + Messaging, MCITP Exchange 2007, MCP, VMWare VCP v2 & v3.
Welcome to the Microsoft Messaging and Mobility User Group: http://www.mmmug.co.uk