Integrating 2 windows 2003 domains to One

Hi Gurus,

We have purchsed another coompany and we need to merge the domains together. Here are the details:

Company A: Mars.mars.com (Windows 2003)
Compnay B CH.ch.com (Windows 2003)

Connection: MPLS connection established

Trust: 2 way forest trust created

Exchnage svrs: 2 seprate one for company A (Exch 2007), Exch 2003 company B

What we need:

1. Have all the mail boxes moved from comany B to company A's Exch server, and company B
2. All company B computers/users to move to company A's domain
3. Since they are trusted now, we are able to see each others network but we need 1 & 2 done in a cost effective and less admin burden.

Thanks