Schedule a batch file to handle this.
This line will delete all files (*.*) in c:\mydirectory that are older than 14 days:
FORFILES -pc:\mydirectory -s -m*.* -d-14 -c"DEL @FILE"
Put that in a text file, rename it to something like "deletefiles.bat" and schedule it.
I haven't tested this, but should be easy enough to try.
EDIT: If you use this, make sure you understand what is happening - the -s flag tells it to recurse the subdirectories, and that may not be what you want to happen. Also, you may need to specify some flags for the DEL command too. :)
EDIT: Realized that you need to download stuff from Microsoft in order for FORFILES to work. I like the accepted solution too, since you don't have to have anything special. The only problem is that it only happens every two weeks instead of running a process daily to remove all things older than 14 days. For what that's worth. :P