Be careful to make sure you have the same architecture on your computer and on your friend's (i.e. 32-bit or 64-bit).
There's some good help here: http://askubuntu.com/questions/974/how-can-i-install-software-or-packages-without-internet-offline
Look a few answers down (ignore the first one about Keryx... too complicated IMHO and unsupported). I did the USB Repository using apt-mirror. It does take a while (depending on your D/L speed), so be patient. Stratus's idea about the /var/cache/apt/archives hack is a good one, but only works if the other system doesn't delete the packages after install/reboot.
There's also a reference to the How To on making your own DVD repositories here: http://ubuntuforums.org/showthread.php?t=352460
It's a bit involved from what I can see, but then you have a DVD copy, albeit outdated pretty quickly, and therefore possibly a waste of time AND money.
Either way, you'll need this https://help.ubuntu.com/community/AptGet/Offline/Repository
information to make sure you set up the repository info in your Software Sources correctly.