Regular Expresson for checking password strength

I want to have a regular expression that check the following criteria are met by $password: - contains at least 6 characters (any) - has at least 1 letter - has at least 1 number - other 6 characters can be anything... I'm happy to work out the structure of a postcode etc, but to be honest I'm still fairly new to working with regular expressions. What the best/easiest way to check whether a variable contains a range? It might be RegExp don't do this? Cheers Nunners