How can I manually install applications on a jailbroken iPad?
Make sure you have appsync and installous from cydia installed on your iPhone, installed from the source
The app has to be a .ipa file.
Place the file in /private/var/mobile/documents/installous/downloads.
Open up installous and install from there.




Or use iPhone Explorer as described in this LifeHacker post:


  Using iPhone Explorer, you can backup or copy apps (and their settings) to your computer or to other iOS device—and it can do all of that without a jailbreak. To backup system files or default applications, like iOS's built-in calendar, you'll have to jailbreak your iOS device. (Even if you're not interested in backing up apps, iPhone Explorer is still great for mounting your iOS device as a disk.)