Hardware :: Read Only File System On External HD

I have a 1TB external HD being used for media. I have it connected to a Mac Mini which until recently was running Snow Leopard Client quite happily. This is my living room media centre. Last week I moved the Mini to SL Server for unrelated reasons. The external drive is now stuck as a "Read-only filesystem". I have tried every method known to Google and man to open the drive to no avail.

Some things you should know:
-The drive is called 'Monkey'
-*any* commands entered with sudo or as root that target Monkey are returned negatively as a result of 'read-only filesystem'. This includes chmod, chown, chflags, etc.
-diskutil cannot modify the volume: 'read-only filesystem'
-vsdbutil cannot modify the volume: something about the automount routine
-running 'ls -alO' produces the following (baffling) echo:
drwxrwxrwx 18 mediacentre staff - 680 27Nov 00:37 Monkey

This means that the volume apparently is fully read-write by all users and does belong to my admin user ("mediacentre") and should be accessible by other users of the machine and there are no flags? No Access? The drive has not been physically jumped to read-only (I even checked in case a housemate way playing a prank) and nothing has changed other than the computer which initially formatted the disk out of the box (i.e. the original owner was 'that' root) has been replaced. I've backed up the disk and am prepared to reformat the dang thing, but I can't even do that, since nothing can target my mystical read-only volume!