Set up a Media Set with enough tapes to hold your 6 weeks worth of backups. Right-click on the Media Set and set the properties to 1008 hours for Overwrite. (24hrs * 7 days * 6 weeks = 1008 hours). However, BE will NOT start overwriting until it runs out of tape space. For example: you have a 100GB tape and backup 1 GB a day. BE will use this tape and APPEND to it for 100 days. Once the tape is full, then it will begin OVERWRITing the data on the tape.
-SQLBill