An easier method to uninstall Rockbox would be to delete the .rockbox folder from the root of the device, delete the H10_20GC.mi4 from the System directoy (you may need to turn on showing hidden files and folders in windows if it's not already on), then rename the Original.mi4 (or OF.mi4) to H10_20GC.mi4. All traces of Rockbox will then be gone completely.
If you're just looking to put songs into the OF's database you could just boot into the OF by holding the back button (the arrow <--) while booting, then connect the device to USB and sync the device with Windows Media Player.