Actually, you will need both. The four core MCSE exams are Installing, Configuring and Administering Windows 2000 Professional, Installing, Configuring and Administering Windows 2000 Server, Implementing and Administering a Windows 2000 Network Infrastucture, and Implementing and Administering a Windows 2000 Directory Services Infrastructure.
For the win2k pro exam you will obviously want to have pro and for the server exam you will obviously want to have server. For the other two, you will probably want to have both (server at the minimum) to do client-server exercises in AD.