How to block USB Pen Drive in Windows XP.

I am a Network Administrator of a Lab which has more than 50 computers of windows XP. I want to Prevent Users from Accessing USB Storage Media like USB HDD, USB Flash Memory, USB Card Reader and USB Mobile Phone Data Cable. But At the Same time I want to Access to access my USB Storage on Every PC. Is it Possible to block USB Pen Drive in Windows XP and Windows 7.
