>These three partitions are formatted
>with the MacOS filesystem.
>
>When i'm running the Mkfs utility, it detects
>only two partions, (MacOS and BSD) so
>i can change the BSD partition type from
>MacOS file system to BSD root and /usr file
>system and format it.
>
>The third partition remains 'invisible' for
>the Mkfs utility so i can not covert it from
>a MacOS to BSD swap partition.
>
>Someone has an idea ?

I believe this is described in the FAQ.  Either re-format the disk with a 
formatter that doesn't have the off-by-one error in the Parition Map or 
create a dummy small fourth partition for MacOS stuff.

-bob