I've changed computer and am currently downloading iTunes again, but!

Will all the songs I've purchased just be gone? Or will I be able to recover them with my Email address?

Is their any way of backing it up because as soon as I plug in my iPod in to the new computer it will sync with iTunes which will have no songs on it thus wiping it.

Any help would be appreciated as I am pretty dumb when it comes to things like this!

i managed to locate mine back that way when i switched laptops before, same with songs i'd purchased via download on play.com

When you plug in your iPod change the setting to manage your music manually and NOT to sync automatically.
I would also suggest downloading software called 'CopyTrans', costs about $20 but well worth it. There'll be free software that does the same no doubt, but this is the one I use. This will allow you to copy, sorry 'back up' the contents of your iPod to your iTunes, and also you can (cough, cough) 'back up' anyone elses iPod's to your iTunes, fully or selectively.
If you back up anyone elses iPod to your iTunes, any music from that iPod will require the original downloaders user id and password to play it on your iTunes, but if you drop it onto your own iPod it will play fine.
Hope this makes sense!

Alternatively, speak to OO, he will direct you to a selection of knock off Nigel websites. The bounder!!

Just as Poolie Barnes said disable the sync auto on your settings, then open the hidden files in your ipod via my computer like you would with an extenal hard drive then copy them from there (will keep all your songs on your ipod). I use my ipod as an extenal hard drive all the time when at mate getting songs I want from their computer, in fact apart from my old cd's that how I got all my music on my ipod