A little background...

I have an online ticketing program. Sometimes shows will have different ticket limits that a user can buy. For example, we have a free concert for Blink 182 coming up but we only want the max tickets "purchased" to be 1 (because they are free, they aren't really purchased but you get the idea).

You will see that in the form the first option is to select a concert, the following drop down is the amount of tickets. Currently, every show has a limit of 8.

If someone chooses a show in the first drop down that has, say, a ticket limit of only 2... then the second drop down should only show a max of 2.

Any help, links to tutorials, whatever would be much appreciated!