Welcome to the site and hope you learn as much as I have. Cab files are apps that install natively on the 6700. So you just download the file on the 6700 and tap to install. Other apps install with .exe files and you install with Activesync via PC. Download to PC and install. It's nice to mod your phone but be wary as some apps don't play well with others, just like the Windows world. So, just because you have alot of space, if the phone is running well, leave it alone. LOL. A nice freeware site is :
http://www.freewarepocketpc.net/