I've downloaded one archiving  utility from Microsoft that enables you
to archive documents by comparing dates. Its a vb program design to
run in the command prompt on the server. You can also edit this
program to accomodate other business process of determining when to
archive documents. You can download this on the Microsoft website

What's the name of the tool????

KVault is certainly a good product in this area but you need to think
about exactly what you want from archiving. For example there is the
spsutil utility in the resource kit that can move 'expired' documents to
a folder outside the workspace which might be all you need.

If you need sophisticated retrieval capabilities of archived info then
you'd need to look at KVault or similar...

SPSUtil...................................