Mandrake 7.2 at least doesn't recognize a -B option to df.  There is a -m
option to show in megabytes, though.

Mandrake 8.2 has a -m option which is just a shortcut to --block_size=
...but "-m MB" shows the list in "977K blocks" (1,000,000 blocks is about
977 * 1024) unlike -m which lists "1M blocks" (1024 * 1024 blocks).

Here are the brief help pages from 7.2 and 8.2 Mandrake.

\\/
http://www.wlindley.com

=============== Mandrake 7.2 ===============

$ df --help
Usage: df [OPTION]... [FILE]...
Show information about the filesystem on which each FILE resides,
or all filesystems by default.

  -a, --all             include filesystems having 0 blocks
      --block-size=SIZE use SIZE-byte blocks
  -h, --human-readable  print sizes in human readable format
			(e.g., 1K 234M 2G)
  -H, --si              likewise, but use powers of 1000 not 1024
  -i, --inodes          list inode information instead of block usage
  -k, --kilobytes       like --block-size=1024
  -l, --local           limit listing to local filesystems
  -m, --megabytes       like --block-size=1048576
      --no-sync         do not invoke sync before getting usage info
			(default)
  -P, --portability     use the POSIX output format
      --sync            invoke sync before getting usage info
  -t, --type=TYPE       limit listing to filesystems of type TYPE
  -T, --print-type      print filesystem type
  -x, --exclude-type=TYPE   limit listing to filesystems not of type TYPE
  -v                    (ignored)
      --help            display this help and exit
      --version         output version information and exit

Report bugs to <bug-fileutils@gnu.org>.

=============== Mandrake 8.2 ===============

$ df --help
Usage: df [OPTION]... [FILE]...
Show information about the filesystem on which each FILE resides,
or all filesystems by default.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all             include filesystems having 0 blocks
  -B, --block-size=SIZE use SIZE-byte blocks
  -h, --human-readable  print sizes in human readable format (e.g., 1K
234M 2G)
  -H, --si              likewise, but use powers of 1000 not 1024
  -i, --inodes          list inode information instead of block usage
  -k                    like --block-size=1K
  -l, --local           limit listing to local filesystems
      --no-sync         do not invoke sync before getting usage info
(default)
  -P, --portability     use the POSIX output format
      --sync            invoke sync before getting usage info
  -t, --type=TYPE       limit listing to filesystems of type TYPE
  -T, --print-type      print filesystem type
  -x, --exclude-type=TYPE   limit listing to filesystems not of type TYPE
  -v                    (ignored)
      --help     display this help and exit
      --version  output version information and exit

SIZE may be (or may be an integer optionally followed by) one of following:
kB 1000, K 1024, MB 1,000,000, M 1,048,576, and so on for G, T, P, E, Z, Y.