I just bought an Aero 4/25 (sounds like a chocolate bar here in
   the UK) and 1.0 reports "unknown density" for the floppy drive then
   panics when it can't ount root (suprised ?)

This means either:

1) The drive isn't configured in the BIOS, so the kernel doesn't know
what size it is.

2) The type field for the drive is `weird'.  In this case it would print
out `fdcN: drive M: unknown device type 0xL0' (where N, M, and L are
variable).