Whenever I try to install something in Installer.app, it gets to "Installing package" and then crashes back to the Home screen! What am I doing wrong?
You likely aren't doing anything wrong. The first partition that Applications reside on has probably just filled up, and Installer.app is crashing because it has nowhere left to put anything. You can use symlinks to move your Applications to another (larger) partition so you can use the rest of the space on your device.
Connect to your iPhone via ssh using either "ssh root@<IPADDRESS>" (Mac) or "putty -ssh root@<IPADDRESS>" (Windows) as above and enter these commands:
* "cd /"
* "cp -rf Applications /private/var/root/"
* "mv Applications Applications.old"
* "ln -s /private/var/root/Applications /Applications"
If you type "ls -la / | grep Applications" now to check whether these commands worked, the final part of the line that's printed should say "Applications -> /private/var/root/Applications". IF it does not say this, STOP and go post in the forum thread with what it does say. If everything looks good, run the following command and then reboot your phone.
* "cd /"
* "rm -rf /Applications.old"