Hi
I have posted below a number of URL links about possible solutions for automating your SQL Express backup - as SQL Management Studio Express does not include a utility to do so.
Do note that below are provided as a courtesy only, we do not recommend one over the other.
http://gatekiller.co.uk/Post/Automate_SQL_Server_Express_Backups
http://www.sqldbatips.com/showarticle.asp?ID=27
http://www.fmsinc.com/free/NewTips/SQL/SQLServerExpressDatabase/Automated_Backup.asp
http://support.microsoft.com/kb/2019698
You can also yourself just do a search online for more results and solutions too!