For this, a ROM image is required. Don't use the ROM transfer programs included with pilot-link on newer Palms, as the programs don't understand the larger ROM sizes. Details are available here . A window will pop up with instructions. Follow these, and a few minutes later you'll have a ROM image on your hard drive.
Developers often have several different ROM images available to test with.
Using unmatched ROM to Device types can be unpredictable, so try to only use appropriate settings. Using a IIIe's ROM under the IIIc hardware doesn't work, for example. You can upload applications and databases from the menu, but you need to reset the device after uploading before they're seen. POSE is a very useful tool, for both Palm developers as well as end users. If an application breaks the rules while running under POSE, the emulation is halted and an informative message is posted as to what went wrong.