Bat file to delete sharepoint backup folders

I've set up an automated backup process for Sharepoint using a bat file to run the stsadm command.  Problem is that it creates a new folder for each backup - so my hd space could quickly become a problem.  

So I need a bat file that will run every week or so to remove those folders.  They all have spbrxxxx format so I'm wondering if there's any way to wildcard the folder name.  

I've been searching thru Google for the past couple of days and haven't found anything useful yet - so any help will be awesome!