Download File Deployer for Liberate
http://www.mediafire.com/?i2z8837d3yxqucr
"Users can use the File Deployer to deploy their own files to use with Liberate. Just add your files to the Content folder, and deploy it. It will run automatically. Your files will be deployed to /Flash2/Files. A shortcut to that folder will appear on the Liberate desktop after running File Deployer, however rebooting will cause the shortcut to disappear. Your files will stay in /Flash2/Files and you will still be able to access them by double-tapping "My Device", "Flash2", then "Files"."
"
Regarding CABs:
To install them, double-click them. Install them to a folder on /Flash2, otherwise the files will disappear after rebooting and they might not even install properly.
If it says there is not enough space, click "no" and install it anyway. If it says that it is not compatible (but the program is supposed to be compatible with ARM), install it anyway.
If it says that it is "not a valid Windows CE setup file", that probably because it is compressed. In that case, you would need to find one that is not compressed, or try extracting the files with MSCEInf and see if they work."