I never had problems with auto configuring geometry.
think it works like this:
sector is smallest part of disk = 512bytes
track is all sectors in one circle (similar to tracks in olympics)
cylinders is track*number_of_heads (try to imagine it, its cylindrical, in 3D, if there are more heads/platters than 1)
I've heard it doesn't really matter what numbers you chose, as long as total number of sectors (heads*cylinders*sectors/track) is less or equal to real disk size.
