need to run external drive on both pc/mac

I've heard that there is a way to format an external hard drive to run on both windows and mac. I'm using a 160g drive in a mac lab (running OS X) at school and then on my PC at home, and I need the files to be accessible to both systems. Can someone tell me what to do? An option somewhere in disk utilities maybe? Even better if the drive doesn't require formatting again...
thanks in adv

I believe mac can read ntfs file system,but I don't think it can write to it, I might be wrong maybe somebody else here can se me straight on that.

Yes, Apple can read ntfs, but not write to it. I believe that you have to use fat32 file format, so that Apple and the PC can write to the file system.