Dear GIJOE

I would like to add a "I'm going/I'm not going" function to the piCal module.
I'm willing to write it myself, but because the maker of the module always knows the best how to change it, I want to ask some help...

Where should I start...?

I want the next:
I have weekly appointments for the members of my orcherstra, and I want them to say wheter or not they are coming to these appointments. So I want to give them a listbox (or some checkboxes) with the coming appointments.
Then they have to select the appointments to which they are NOT going.
Then, that information has to be stored in the database. And the day before each appointment, a list with the "not-coming-members" has to be sent to someone...

Thanks in advance!