Fri Oct 12, 2012 6:14 pm
You don't format it to anything; when you write the image it will make the partitions in the correct format.
If you're interested in knowing anyway, I believe the boot partition can be either FAT16 or FAT32 (not 100% sure though) and generally the Linux partition is in ext4.
{sig} Setup: Original version Raspberry Pi (B, rev1, 256MB), Dell 2001FP monitor (1600x1200), 8GB Class 4 SD Card with Raspbian and XBMC, DD-WRT wireless bridge