You may need to "massage" the ROM file using VTI on your desktop computer before loading it into the emulator on the Axim.
From the
Freewareppc download page for it (sorry for their embedded links):
"NOTE:
There is a bug that in some cases doesn't allow the TI85 rom to function, all you need to do is with the VTI in the
Desktop PC create a .sav file from the TI85 rom (just use the rom and right click "Exit and save state"), then copy this file to the
Pocket PC with the same name that has the TI85 rom file."
You may need to do something similar to your TI-83 ROM.
The emulator is not certified compatible with Windows Mobile 5 but it might work fine.