Did you follow the install instructions for SFC OP?
1. TURN OFF ANTI-VIRUS
2. INSTALL OP, SAY NO TO GAMESPY ARCADE SETUP AND NO TO DIRECTX 7
3. PATCH WITH V2.5.5.2
ftp://www.dynaverse.net/sfc2_op/patches/SFCOP_Patch_2500-2552.exe4. MAKE SHORTCUT TO POINT TO THE STARFLEETOP.EXE GAME FILE, SFCOP.EXE FILE IS BROKEN
5. INSTALL THE DIRECTORY SERVER FIX
ftp://www.dynaverse.net/sfc2_op/patches/sfc2_directory_server_updater.exe4. INSTALL FIRESOUL'S OP+ V4.0
ftp://ftp.xenocorp.net/game_files/Star_Trek/starfleet_command/Starfleet_Command_OP/shiplists/opplus_40_models.exe MODELED VERSION
ftp://ftp.xenocorp.net/game_files/Star_Trek/starfleet_command/Starfleet_Command_OP/shiplists/opplus_40_no_models.exe NO MODEL VERSION
6. INSTALL THE AOTK4 INSTALLER ALLOWING FOR DOS WINDOW TO CLOSE ON ITS OWN
http://xenocorp.net/downloads/game_files/Star_Trek/starfleet_command/Starfleet_Command_OP/Campaigns/AotK_V/AOTK4.exe7. INSTALL LATEST VERSION OF DIRECTX LOCATED AT
http://www.microsoft.com/downloads/details.aspx?FamilyId=740AC79A-5B72-447D-84F9-EE6407ED1A91&displaylang=en WHEN YOU RUN THIS FILE, IT WILL ASK TO EXTRACT TO A DIRECTORY, POINT TO A LOCATION THAT YOU KNOW, LIKE 'MY DOCUMENTS' AND CREATE A NEW FOLDER. AFTER EXTRACTION, GO INTO NEW FOLDER AND RUN SETUP.EXE. AFTER DIRECTX INSTALLS, DELETE FOLDER AND RESTART SYSTEM.
8. MAKE SURE YOUR VIDEO DRIVERS ARE LATEST VERSION
9. TURN OFF FIREWALL OR CONFIGURE CORRECTLY FOR SFC-OP
10. WHEN DONE PLAYING TURN ANTI-VIRUS BACK ON
11. WHEN GOING TO PLAY AGAIN, TURN ANTI-VIRUS BACK OFF
ALSO MAKE SURE YOU ARE RUNNING XP
VISTA LAGS SEVERELY ON THE DYNAVERSE 2 SERVERS .... USE VISTA ONLY FOR SINGLE PLAYER, GAMESPY ARCADE OR LAN PARTY ONLY, NOT DYNAVERSE 2
maybe you missed one of the install steps.. most people skip step 1 which breaks the game.
If you have Vista, please state as such and I can give you install instructions for Vista, however D2 will be almost unplayable.. so it would only be for Gamespy Arcade, Lan parties or Single Player.