The folks at MSSQLTips have some very helpful articles, the one most relevant for this is "Automating SQL Server 2005 Express Backups and Deletion of Older Backup Files"
The basic approach is to set up two tasks using the Windows Task Scheduler. One task runs a TSQL script that generates separate backup files for all MSSQL databases (except TEMPDB) with the database name and a date/time stamp in the file name into a specified directory. The second task runs a VBScript script that goes through that directory and deletes all files with a .BAK extension that are more than 3 days old.
Both scripts require minor editing for your environment (paths, how long to keep those database dumps) but are very close to drop-in-and-run.
Note that there are possible security implications if you're sloppy with these or with directory permissions, since they are plain text files that will need to run with some level of privilege. Don't be sloppy.