Merging two NT 4.0 networks

The company I work for is merging with a sister company. Both sides are running NT 4.0/DHCP/WINS and we are connected via routers and a FracT1. Each site has it’s own subnet mask, PDC/BDC’s and domain names. Both sites use Lotus Notes and I currently access the Inet, do Notes mail routing/replication through the sister company.

We are looking to merge the two networks into a single domain model because within a year or so we’ll be thrown together in one building. One site will have a PDC/BDC while the other settles with just a BDC.

What’s the best way to take a two domains and combine them into one?