The photo sync is one way - computer to iphone.
Pictures taken with the iphone can be imported as with any digital camera.
The iphone will sync pics and music with one and only one computer. When you sync to another, it will first erase the current content and replace with content from the new computer.
If you sync contacts/calendars to a blank computer, then they will be erased as well.
It has always been very basic to always maintain a backup copy of your computer files/docs/pics/music/etc. Use your backup copy to put everything on the new computer.
There are some 3rd party utilities that provide for transferring these photos in the opposite direction which are not supported by Apple and the original resolution of these photos will be lost. Photos transferred from your computer are optimized for viewing on the iPhone as part of the iTunes sync/transfer process - the original resolution of these photos is reduced. The iPhone is not designed or intended to be used as a backup storage device.
Here is one such utility.
did this solve it?
I have slightly different problem...
I have just upgraded my iphone 4 to have the 5 OS thingy and the album that I transfered to the phone when i got it, which had old pix and some camera photo's is now gone leaving just the iphone album.
when i go back in to the photo tab and tick transfer photo's and "apply" it comes up with the exact same message you had Todd.
Will it delete the old transfer album or delete all 450 photos I have taken on the phone?
Hoping it will just replace the old album???!!!!!