MikkoPPC creates word completion data for PocketPCs. It uses plain text lists, to create a "dyncompdict.dat" file. This file may then be placed in your PDA's "Windows" folder.
Thus, MikkoPPC provides a way to create your own word completion dictionary.
MikkoPPC has been tested successfully on an iPaq HP 2210 with PocketPC 2003, but should work with other PDAs and PocketPCs that use the "dyncompdict.dat" file.