The model has to have exactly the same number of limbs and other data for DB to make it work ( otherwise it has a fit and brings up errors ).
What you should do, is if the first model ( GI/H-GI-Move.3ds ) has say 54 frames, then you use the Append Object command on the second model, so that it's start frame is at frame 55 ( one after the first one ).
If you still have some issues, post the error message that you are getting and hopefully I'll be able to help you further.
Hope I Helped...
Jess.

Team EOD :: Programmer/Logical Engineer/All-Round Nice Guy