I've joined a 2003 domain with SUSE 10.1, no problem.
Just ensure that you use the fully qualified domain name (like microsoft.com) instead of the NetBIOS domain name when you enter the domain name.
Make sure you have DNS properly set up.
Also, when you're prompted to enter credentials for an account with rights to add the machine to the domain, do NOT use the domain\username syntax. Just enter your domain username (like bobw) for the username; it will infer the domain name from the domain you are joining.
Cheers!