Now that OS X Snow Leopard supports exfat / fat64 and Microsoft Windows theoretically does, you might naively assume that you can share external drives between Vista and Snow Leopard. This is true with one giant caveat: you can’t format the drive on your Mac. You have to format it first on your windows box due to some unknown issue from the morons from Redmond. Posted to hopefully save you the two hours I wasted debugging this. Of course, if you say, already have 300+GB of data on your external drive that you originally formatted on a mac, this knowledge isn’t the most helpful thing ever. Sigh.