Hewlett Packard did release the roms for a number of their calculator roms to the public, and the hp48 is one of the ones they released. The link you provided was for a 2.5mg download so I didn't bother checking it out. I know that the original version of emu48 didn't work well with the 2003 os. I sugest that you search the following web site for the most recent version: http://www.hpcalc.org/
I have it running fine on my iPaq and if you have more problems post them here and I will try to help. But before you go any farther check and see that your Pocket PC's processor type is supported.