In 2005 - you have to add the Maintenance Cleanup Task to the maintenance plan and configure it. Sounds to me like that does not exist in the plan and that is why you are not seeing the files cleaned up.
You will need two tasks - one for backup files and one for transaction log backup files.
Jeffrey Williams
“We are all faced with a series of great opportunities brilliantly disguised as impossible situations.”
― Charles R. Swindoll
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Managing Transaction Logs