Cant transfer photos from computer to iPhone 3G

Hello,
Ive recently not been able to transfer photos from my iPhone picture folder on my computer to my phone. Ive done this before and it worked. Was it an update that has caused my pictures NOT to show on my phone? Ive selected the folder to be synched on iTunes and nothing will get transferred, even though there is an iPhone photo cache folder created after I synchronize my phone with iTunes.
Help?
iPhone software 3.1.2, running OSX 10.5.8 and iTunes 9.0.2
MacBook Pro 15" Mac OS X (10.5.8)