Latest Steam version or GOG versions will allow you to play the campaign and official DLCs. We host a Multiplayer server for the NicksCOOP mod. It works with the original campaign and Corkscrew Rules russian content. Steam / GOG:  
An UpdateServer with a filter for spammy servers. Install instructions at http://wiki.333networks.com/?title=UpdateServerAddress. Normally pasting two lines into UnrealTournament.ini
Our server syncs with main list every 10 minutes or so for new servers and hides servers that show misleading player count.
Uninstall is reverse of install, delete those two lines. If you already use custom masterservers add psinet.333networks.com in first placement with bFallbackFactories=True and bKeepMasterserver=True http://wiki.333networks.com/?title=Adding_Individual_MasterServers_Manually