Ext Hard Drive turned in a Mac Disk

I have a problem, I have used my WB External Hard Drive to copy my Macintosh HD using Time Machine. Everything was succesful, it works and Mac OS X recognizes the Hard Drive as Time Machine. The problem is when I plug it in my PC on the University (Windows XP) it doesnt recognize it! I cannot install MacDrive on this PC because it is owned by the University so I need an other solution. I think I lost some important software when my Macintosh used the external hard drive as a Time Machine. Is it possible to turn this the other way around again so I could use the external hard disk like I use my USBstick (on both Macintosh and Windows XP) as a Mass Storage Device? Please help! What to do? Im not really that computer savvy so if someone would guide me what to do step by step i would be very grateful! Thanks!