Once you have created a CABfile, you'll want to get it onto the target device.

You can of course write another application to achieve this, but if you are lazy like me, you can use a free product like this:

*EZ Setup by spb Software House

If you would like to install your device application CABfile from an MSI file on the desktop, checkout the following:
*For detailed step-by-step instructions including sample code checkout Deploying .NET Compact Framework 2.0 Applications with .cab and .msi Filescf2appscabmsi.asp
*For an overview including sampe code checkout Installing a Windows Mobile device application from a desktop MSI

CAB Repositories
You can download and contribute a lot of free applications as CAB-files on the following resources:
*Pocket PC Freeware Community
*Smartphone Freeware Community