Windows 2000 server domain to Windowsw 2008 server domain is the same process as Windows 2003 to Windows 2008 server. Like leew said you would need to prep your domain with adprep.
If you are going to Windows 2008 server R2 then make sure you are using the adprep32 of the R2 DVD to upgrade your schema.
Migrating your 2000 to 2008 domain is fully supportable. I have done multiple myself.
Like leew said make sure you run dcdiag and netdiag before promotion. Run dcdiag on Windows 2008 server after promotion.
Step by step guide for 2003 to 2008 which is the same for 2000.
http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/Windows_Server_2008/Q_23665224.html
