It can't have formatted the whole disk (though I was worrked at the time),
because both Linuxes still boot fine. Windows' C: partition is perfectly
readable and writable by Linux, and is empty.
In case it's still of interest, this is the output of fdisk -l:
Disk /dev/hda: 80.0 GB, 80054059008 bytes
16 heads, 63 sectors/track, 155114 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 24975 12586896 c W95 FAT32 (LBA)
/dev/hda2 25022 111563 43617168 5 Extended