I have not used 3.7 but I know mqx 3.8 has an example in program files\fresscale mqx 3.8\mfs\examples\sdcard. I have used this code to read/write to sdcard or microsd cards. There are build projects there for IAR or Codewarrior.
I have only used the USB as device mode connected to a PC. There is an mqx example for usb\host\examples\msd that should help you.