Creating kMDMattsCoolMetadata?

[Matt Johnston]

Hi Guys,

I've been reading around the subject and finding there's not much out  
there for creating, for example, kMDMattsCoolMetadata and assigning  
it to a file so, for example, I then should get:

blancmange:~/Desktop wibble$ mdls LittleFile.txt
LittleFile.txt -------------
kMDItemAttributeChangeDate = 2007-02-08 22:47:14 +0000
kMDItemFSContentChangeDate = 2007-02-08 22:47:31 +0000
kMDItemFSCreationDate      = 2007-02-08 22:47:31 +0000
kMDItemFSCreatorCode       = 0
kMDItemFSFinderFlags       = 0
kMDItemFSInvisible         = 0
kMDItemFSIsExtensionHidden = 0
kMDItemFSLabel             = 0
kMDItemFSName              = "LittleFile.txt"
kMDItemFSNodeCount         = 0
kMDItemFSOwnerGroupID      = 501
kMDItemFSOwnerUserID       = 501
kMDItemFSSize              = 0
kMDItemFSTypeCode          = 0
kMDItemID                  = 2042666
kMDItemLastUsedDate        = 2007-02-08 22:47:31 +0000
kMDItemUsedDates           = (2007-02-08 22:47:31 +0000)
kMDMattsCoolMetadata    = Hello Mum
blancmange:~/Desktop wibble$

There's a heap of stuff on CocoaDev - but seems to be a lot of people  
asking the same question. We can read the stores, but how do we just  
set a single metadata item?

Can anyone either put me out of my misery or point me at a helpful  
article?

Thanks in advance,

Matt