My laptop crashed about 6 months ago, (beyond repair) I stupidly hadn't backed up itunes but a friend who is a bit of a tech wiz managed to salvage it and back it up for me.
I've finally bought another laptop and installed itunes but if I sync my iphone will it delete everything on it as my friend now can't find the disc she backed it up to so I can't restore itunes.
So, if I do sync my iphone, what will happen? I've bought a few apps since and don't want to lose them, I mainly want the back up as I'd uploaded tons of cds and I don't want to have to do that again as it took ages. If friend finds the discwith the music on, can I restore the music and sync again and still not lose the apps?
I'm not sure what will happen to the apps, but if you sync your iPhone to another computer it will erase the other contents. Apple have designed the iPhone (and iPod) to prevent you from copying content from it back to a computer. I'm not sure if you can re-download the apps without paying again. You can't do that with music, videos etc. (iTunes will just tell you that you've already downloaded them.)
You can use third party software (such as this, BTW haven't tried it myself!) to backup the content to your new PC before you sync with iTunes. There's some instructions here. If you find the disc with the backup on, then there are ways of restoring it before you sync your phone with the new computer.
AFAIK you can't copy apps from an iPhone without jailbreaking it.
You can redownload your apps if it all goes pearshaped. It will appear like you have to pay again but when you click install, it will tell you that you've already purchased this and if you'd like to just download it again.
Viva, back it up man! It's a royal pain in the ass if it goes wrong. Choose to copy all files to itunes media folder option so all your MP3's are in the same place. Make's life a lot easier to backup.