Windows 2003 Trusts

I have two domains:
xyz.com
abc.com

They are all within the same network, abc.com was just created for operations to separate the servers.

This is a windows 2003 network, and maybe within those domains a few windows 2000 servers.

Since there are transitive trusts automatically created do I need to create any trusts, or due to transitive trust?

Or do I have to create a local group and put it in a global group, etc.

Thanks