I think most of the programs in the HP Museum FTP site are for older calculators. There are some other websites dedicated to the 48 series (one website is hpcalc.org) that have a LOT of downloadable software that can be brought into the calculator fairly easily (compared to the older calculators) because of the RS-232 port. You just need a cable to connect it to your PC, the cable is easy to find for sale but might use a hard-to-find connector making it a little hard to build your own.
if you have a laptop or other computer with infrared, don't forget that you cna do serial transfers with the built in infrared port on the 48SX.(which I still claim has a better interface than the GX)
Does anyone have experience with using the infrared ports on Palm devices to transfer programs to the HP-48GX?