iPod touch Can I not get songs off my friend's computer using his itunes?

You need to disable auto-sync.

Once it's on a manual synch, you'll be able to add music regardless of whose iTunes it's coming from. HOWEVER iTunes-purchased music will not play on the computer through any non-authorized iTunes accounts. But if you don't mind listening to those songs on your iPod through headphones and speakers, you're fine.

I had the same problem where it deleted all my songs and replaced them with his. Is it possible to upload other peoples music onto your ipod from their comp?

Disable Automatic syncing and you can add music to your ipod from multiple computers.

1.Plug in ipod
2.Open iTunes
3.Tick the box for 'Manually manage music and videos'
4.You will have to re-synch all your content from iTunes over to your iPod again.
5.Go to music, select all and drag onto your ipod.
6.Repeat with videos etc.

Repeat steps 5-6 for any other computers.