Just so all you new iPhone 4 owners know, you will need to have at least Apple OSX 10.5 to be able to Sync properly with iTunes 9.2. If you own a PC with WindowsXP/7/Vista, you don’t require anything other than iTunes 9.2. Which seems kinda funny 
For Mac users, the iPhone 3G and 3GS required OS 10.4 to sync. And while we’re a little late on reporting it, we know it will affect some users all the same. iPhone 4 requires OS 10.5.For many of us, it doesn’t matter. We’re on OS 10.6 by now. But there’s no real logic as to why, if older OSs can run iTunes, they can’t sync with new iPhones…especially when you look at how well Apple supports iPhones on the PC. You can sync an iPhone 4 to any PC running Windows 7, Windows Vista, or Windows XP (SP3).
Source: http://gizmodo.com/5572984/we-missed-this-iphone-4-requires-os-1058