My Mac hard disk died, so I replaced it and installed OS X Leopard 10.5.8. Problem now, iTunes doesn't see my iPhone 3GS at all. iPhoto works just fine, but iTunes is blind. I have too much info on my iPhone, I don't wish to restore/reset it and wish to get everything from my iPhone sync'd into iTunes afresh. How can I do that?
Try to restart your iPhone. It is done by the holding the power button (the one on the top right of the case) for about 10 seconds. Then plug it back to your Mac.
If it still doesn't work, try to reset your iPhone, by holding the power and the home button at the same time for about 10 seconds.
Don't worry either way won't erase any personal information.
More info on Restart : http://ipod.about.com/od/iphonehowtos/qt/turn_off_iphone.htm
Make sure you have iTunes 9.1.1 (or later) installed.
Also, I don't know if there is an easy way to get your data from your iPhone into a clean iTunes library. If you didn't copy over your iTunes library from your backup, then iTunes won't recognize that it's ever worked with your iPhone before, and will only offer to wipe your iPhone and start over.