Had you included your iTunes library with your computer's backup (along with all other important data) per the simple instructions included with this link, this wouldn't be a problem.
Your iPhone will not be completely erased. What will happen will be just as the warning message indicates - all iTunes content will be erased from your iPhone with the first sync.
Thanks for the reply. much appreciated.
I hadn't given my phone a thought before I re-installed, my itunes installation is the same with all the same music and video's and my phone backed up OK when I connected it last week.
Do you think it will be OK to back it up again and then just erase when it prompts me and then restore from the backup it just did?
No iTunes content is included with the iPhone's backup - no music, movies, TV shows, audio and print books, tones, podcasts, and apps. All iTunes content on your iPhone should be in your iTunes library on your computer, and your iTunes library on your computer should be included with your computer's backup along with all other important data - documents, photos, etc.
Since your iTunes library on your computer has been erased, restoring your iPhone from the iPhone's backup changes nothing in this regard since no iTunes content is included with the iPhone's backup.
The entire iPhone is not erased in this situation - just iTunes content as the warning message indicates.
You can redownload iTunes purchased content from the iTunes Store without having to pay for it again. iTunes also includes an option to transfer iTunes content that was purchased/downloaded from the iTunes Store from an iPod or iOS device. First you need to reauthorize your computer with your iTunes account with iTunes if you haven't already done so. With your iPhone connected and without syncing, at the iTunes menu bar do to File and select Transfer Purchases From - the name of your iPhone.
Thanks again so much for replying.
Just so I am clear, the phone in its current state (with the exception of media - music, vids, podcasts, ringtones) will be backed up to my new Win 7 installation. Once I choose sync and I get the erase warning, my iphone will then be erased and restored via this recent back to its current state but without the media stated above?
I then need to re-add the music, vids, etc.
Can I ask if the installed apps and their positions within my phone will be restored too or will I need to download them all again?
Posting this so hopefully it will help others.
I found a post which suggested changing the persistant ID for iTunes but that didn't work so here is what I did, I can now drag music and video's to my phone.
1. Backed up phone
2. Checked the box that said 'Manually manage music and movies'
3. Clicked on apply when asked to apply settings
4. Got the message asking if I want to erase the phones contents and sync with this installation of itunes
5. I clicked on OK (a bit scared here but went for it) and I could see iTunes 'processing' in the iTunes status bar and then that was it, nothing really happened. I picked up my phone (4s in case you're wondering running IOS 5 - might install 6 this week, don't have a reason to upgrade to 6 as yet) and it was exactly as it was.
6. This process to about 30 seconds and nothing was deleted or anything
I rebuilt my itunes library and am working again just fine.
Hope this helps someone