I hope this works for you but here is how I do it. Make sure you have the correct USB drivers (you can get them from the samsung website)

1. Plug in usb cable to computer then phone (as wierd as this sounds try all of your USB ports, for some reason this doesn't work on my front ports)

2. Select mass storage

3. pull down task bar from top of screen and where is has USB connected select it and pick mount

4. You should get either 1 or 2 auto play options (1 for the internal SD card and 1 for the external SD card if you have one)

5. Pick Open Folder To View Files for one or both and you shoud see the directory structure for internal and external(if you have) SD cards.

Let me know if this works, I think there are other ways to do this without rooting the phone, but make sure you try different USB ports sometimes mine works and sometimes I have to try a different one,

FYI, I am running Windows 7 64-bit 

mwjack