Go to the game menu and go three steps up and you'll see the Saved Data Utility (PS3)
find your GT5 save and press /\ and hit copy.
Then you'll be asked to where you want to save it (It shows users and external devices)
Just select the Memory Stick USB and it will copy it to it.
It will save the save file in X:\PS3\SAVEDATA\blablabla-GAME
