Migrating from old w2k domain to new w2k3 domain

We are currently running with a w2k domain, however the domain name appears to be giving us lots of problem because it is not a supported domain name, for example our domain name currently is (ABC_1). We have purchased a new w2k3 server that will replace the old w2k dc. I am new to this and want to make sure i have all the steps needed to do this. The server name will change and so will the domain name.

I currently have a test network setup with 2 servers one being w2k and the other w2k3 but am kinda stuck on what I need to do next to test.

Thanks in advance for any help.