How to Erase a Disk with a Corrupt Apple Partition Map?

I have a 40GB disk that I pulled from an old iMac and put in an external Firewire drive enclosure. The partition map is corrupt and claims that the disk size is 2 TB (yeah, I wish!).

Is there a way to simply erase the disk and partition map so I can just start again with it? Disk Utility will show the disk mounted but can't repartition it. I've tried pdisk and that coughs up a floating point error. I've tried using iPartition (although I think that uses pdisk under the covers) and that can't handle it. I'm not looking to salvage any data, just wipe the drive so I can start from scratch.

Thanks in advance,

Stu