Ump2 is made up of 3 parts maybe you have not followed the instructions carefully.
In any case the only difference when starting avp2 with ump2 being the loading screen
If properly installed the change screen.
I do not know if you are using the tbbc client to connect multiplayer, in any case the command to start avp2 with ump2 be the same -rez ump2.
You can either start it from the main game menu, or from the optional parametersinside avp2 client .