I have a Macbook with Snow Leopard and a Samsung 640 GB external hard drive. I want to split the external hard drive to use as time machine and file transferring with Windows. How can I do that?
You should be able do this with the Mac's Disk Utility. Just be sure that the partition that you wish to use on Windows you set the format as MS-DOS.
There's a very detailed guide on how to do that on Leopard/Tiger: