MPC connected to PC - PC not recognising it as a drive

I have just bought an MPC 500 and am having problems with my PC recognising it when it is connected.
My MPC is saying USB: Connected, my PC recognises there is a USB connected, but it does not show up as a drive in Windows Explorer (i.e. i have C: drive etc but the MPC does not show up as a : drive) therefore i cant drop any of my samples onto my MPC memory card which means i cant start making beats with my new toy!!
Note in Device Manager the PC tells me that the MPC is connected as a USB Hub - i just cant see it!
I am using XP but am also having the problem on a friends laptop with Vista.

Any help would be much appreciated!!

Put the cf into MPC and then connect, should show up as external memory

cheers guys i had the card in....but not far enough! works sweet now.... except for the embarrassment.