Copy "UPX4PPC.exe" over to the Pocket PC on any folder.
Also copy "upx.exe" over to the same folder.
And copy "gsgetfile.dll" and place it in the "\Windows\" folder.
After that, you can just run UPX4PPC right away.
If you need the application to show up in Start Menu, you will have to create a shortcut manually.

Note: The CAB file is downloadable from http://mobile-sg.com/ppc/apps/