To get text to appear in the Memo section of Palm Desktop, you need to use a program that uses the Palm OS Memo database; i.e. the built-in Memo Pad, Memo Plus, or similar ...
SmartDoc files are backed up along with many other Palm databases in ~/Documents/Palm/Users/<your user name>/Backups/ (on Mac OS X). You need a program such as the free PorDiBle to convert the *.pdb file to a *.txt file and back again.
Sound convoluted and un-mac-like? It is; but it works.
If you want a better and more integrated solution, use WordSmith. The conduit supplied for this software is a lot better; it automatically creates *.rtf files in a directory of your choosing.
if you want a free solution then try Documents to Go if it's bundled with your Palm or just stick to writing a quick memo.
Hope this helps.
Stephen