It doesn't work because it is a string field and not a native date field. An inherent issue with some date fields in LANDesk. I put together an ER for this - http://community.landesk.com/support/thread/10278
If you vote we can change this. ;-)
You can do this, but not very easy. You need to use string regex stuff like [0-9] to represent numbers - http://www.droppedpackets.org/reports/use-regular-expressions-in-queries/
This article goes into how to use reg expressions to achieve what you want.. It is tedious and a pain.. ;-)
Just a guess since I'm not near a console is that the information may be stored in SQL as a text filed not a date field. If this is the case you will have to use either SQL or the LANDesk report writer (Excel) to complete this. LOL - I gues I should refresh my screen once in a while - it is varchar.