The first question is regarding the bar code log in...
I am guessing that you are referring to the fact that when a member of the club comes to work out, they will present their card at the front desk which will then get scanned; is that correct?
If that is the case, you then need to know the capabilities of the bar code machine and software. I don't want to assume too much, but my guess is that it is a typical bar code scanner/gun that the attendant has - and is hooked up to a computer with the software drivers for the scanner.
First, find out what information is actually put on the bar code of the cards. Hopefully, it would be the same number as their user id in the database that your managing.
If that's the case, you would first need to see if the bar code scanner can output the user ID into a PHP application - either through xml or even a text file. Then in your PHP application, you would need to query the database where equal to that bar code ID to see if the member is valid. This would also mean that there would have to be some field in the database table that confirmed if the user was valid (active, paid up, etc.). It could even be a BOOLEAN value... meaning when the user has paid their dues or whatever, you could have a column titled userActive, for example - and it would get updated to TRUE if their account is current and it gets updated to FALSE if they don't make a payment. So, then you would get the user ID from the bar code and then query to get the results of the aforementioned "userActive" column... if it is TRUE, than you would let the user in. If it's false, then you would send them home :).
If you have any more details, post them and I will see how I can help.