iTunes won't let me sync my iPod when it is disabled

Welcome to the discussions,
You can only sync to one computer at a time. If you switch, all media content will be erased and replaced with the content of the new iTunes library. So to prevent a sync, disable autosync in iTunes/settings/devices before you connect.
Is your ipod showing up in iTunes? If not, is Apple Mobile Device Service still active? http://support.apple.com/kb/TS1567
Are the drivers installed? http://support.apple.com/kb/TS1538
If your ipod shows up in iTunes, back up manually and transfer your purchases, here's how to:
Make sure your new computer is authorized in iTunes. Disable autosync in itunes, connect your ipod, right click on it in the device list and choose backup.
This will save data, pictures and settings to itunes. See what's included in this backup here: http://support.apple.com/kb/HT1766
Transfer your purchases the same way to copy all apps and bought media from the Store to your computer.
Set up at least one contact and event on your computer to be able the merge your calendars and contacts after your ipod got wiped during the first sync.
The rest of the data can be restored from the backup you made.
Restoring: http://support.apple.com/kb/HT1414
Music is one way only, from the computer to your device, unless you bought the songs in itunes and transferred your purchases.
There is 3rd party software out there, but not supported by Apple, see this thread: http://discussions.apple.com/thread.jspa?threadID=2013615&tstart=0

The only other way to disable an ipod is putting a passcode on it. In that case, if you don't know the code, you'll have to restore it "as new ipod". See this article: http://support.apple.com/kb/HT1212
To make iTunes recognize your ipod, try to connect in recovery mode: http://support.apple.com/kb/HT1808

You're welcome, and tell your friend that locking ipods is not funny at all 🙂