2003 32/64 domain migration to 2008

This is more of a confirmation than a question but here goes:

We have two domains for sake of this question call them domain1 and domain2. Both DCs for these domains are 2003 32bit and there is a one way trust between domain 1 and 2 (Machines on domain 1 cannot authenticate to domain 2 but it works the other way. The add a little more complexity on domain1 there is a 64 Bit 2003 server running exchnage 2007 on domain1. there are a total of 8 servers mostlty standard edition and 1 enterprise edition (mostly on domain 1 running as member servers only)
Ok now the question we want to move to a 2008 domain (ideally 64Bit)
We have a new 2008 64 bit server that is just sitting as  standalone (in a workgroup) at the moment and i am trying to get clear in my head the next steps.

Firstly can we just migrate domain1 or do I need to to do both? (domain 2 is hopefully being phased out over the next few years)

Im presuming as far 32bit/64bit goes  i will need to run adprep from a 2008 32 DVD on the 2003 32bit DC's then will need to run adprep from 2008 64 DVD on the exchange host which is 2003 64.

all these servers are Virtual machines on vmware ESXi so i was thinking of taking entire network offline and snapshoting the main dc so that if all goes wrong i can restore before any replication takes place.

The overall plan to begin with is to be able to add 2 new 2008 64bit member servers (for Terminal Services and Application serving with the longer term goal of moving the DC's and all other server roles over to 2008 in readyness for Windows 7 deployment

Any advice appreciated as i have been researching this for weeks and have found conflicting information about 32bit/64bit mixed domains.