calendar control with appointment application

Hi,

I'm using a calendar control in my page to allow clients to pick a date and schedule an appointment. I have a simple database for now that consists of two tables: Clients and Appointments and I'm using Linq to Entities.

I want to disable the date in the calendar where there are 5 appointments scheduled for already so that clients can't select it. I know how to manipulate the calendar with the day_render event and how to disable hardcoded dates, What I'm having problem with is how to approach and implement this requirement.

Another table in the db?(I'm really bad at db design) Linq Count function?

Basically I'm looking for suggestions, tips, code help c# or vb.

Thanks