Migrating from Server Standard 2003 to SBS 2011 on a different domain

Hi --

I have a Windows Server 2003 Standard box running Exchange 2003 Standard (on the same box) managing about 50 users and 40 PCs. I want to migrate the users and mailboxes to a new SBS 2011 Standard box we're in the process of installing. But:

1) In the process, we'll be redoing their network infrastructure. The two servers are currently on different networks. Once the new server is ready to go online, all other computer equipment will be moved to the new network.

2) The servers are running different AD domains.

Where do I go for pertinent information on migrating this system? Most of what I have found involves migrating from one version of SBS to another, and this is not the case here. But also, I have the domain name change to contend with.

Thanks
CL