The honest answer is: maybe.

Many programs that you buy have registration codes, so save all of those. If you get a new PDA (assuming that it uses the same format-i.e. Palm OS vs Windows Mobile for example) you usually can load the programs onto the new PDA then activate them with your registration code. If that doesnt work, I have contacted the "owner" of the program I bought and told them I would like to load it onto my new PDA and usually they will then send a new registration code (after they check their records to make sure you bought it).