Welcome to the forum!
Unfortunately 'remove programs' is the only official way to uninstall something on a PPC. There are several utilities that do a better job but they need to be installed before you install the program so they can monitor the installation and record the changes.
Was wifi companion running when you tried to uninstall it? That might have prevented the system from deleting some files.
To my knowledge you now have two choices:
1. Manually fined all files still on the device and delete them (they could be under windows, windows\startup, or in program files\AppName
You should also get a registry editor, search for any keys containing the app name and delete them.
2. Never tried it but it should work: reinstall the app, make sure its not running then uninstall again. If the files were not deleted because they were in use the first time this should solve the problem.
There is a third option but its quite inconvenient: Back up your data and hard reset the device. Its guaranteed to get reed of everything. :wink: