Backwards Syncing Possible iPhone 3G

First you need to re-authorize your computer with your iTunes account with iTunes.
With your iPhone connected and without syncing, at the iTunes menu bar go to File and select Transfer Purchases From - the name of your iPhone. This will transfer iTunes content that was purchased/downloaded from the iTunes store only. If a 3rd party app on your iPhone is not transferred, you can re-download the app with iTunes on your computer and you wont be charged again for a purchased app as long as you use the same iTunes account to re-download the app that was used to purchase the app originally.
To transfer iTunes content that was not purchased/downloaded from the iTunes store, there are some 3rd party paid utilities that provide for this, but such utilities are not supported by Apple. The same for photos that were transferred from your computer to your iPhone via the iTunes sync process if these photos are not included with your computers backup along with all other important data on your computers hard drive. Photos transferred from your computer to your iPhone are optimized for viewing on your iPhone as part of the iTunes sync/transfer process - the original resolution of these photos is reduced on your iPhone. The original resolution of these photos will be lost when transferring these photos in the opposite direction with a 3rd party paid utility that provides for this.
The iPhone is not designed or intended to be a backup storage device.
 MacBook Pro 15" Intel Core 2 Duo/2.53GHz/4GB RAM/500GB HD Mac OS X (10.6.2)  iPod w/Video 30GB,  iPhone 3G 16GB

You can transfer your purchased content from the iPhone to your iTunes library:
http://support.apple.com/kb/HT1848
The other content will have to be re-imported. Or you can try a third party program like Pod to PC