Calculated field(s); How-To? I'm just missing the whole boat . . .

I am working on what seemed to be a simple task at first, now I'm stuck. What I have so far;

- Event Registration (CCK Node Type)
- - Title: Your name
- - Event Name: (node reference)
- - Group size: (integer)
- - Your email Address: (email)

- Signup_Limit (CCK Node Type)
- - Event Name: (node reference)
- - maximum_capacity: (integer)

Now I create an event (makes it visiable in node reference) and create the signup limit (maximum seating capacity). That fulfills the backend.

I make registration available . . . 5 people sign up with 4 people in each group = 20-people.

What I would L I K E to do is .. .. .. .. 'everytime someone registers their group (group size) it is subtracted from the maximum_capacity'. I never really saw this as 'actually' subtracting it, rather using views to perform the visual along with filters. This would give the event organizer an Idea of the seating capacity status at any given moment based on registrations.

So I have attempted to use a calculated field in the signup limit node type - no joy.
I attempted to (sum) all listing of group size in views - no joy.

Really, right now I think I am just confused and frustrated = Lost Focus }8-Q if you know what i mean . . .

So, I am asking if anyone has attempted/accomplished this? Am I making it TOO difficult? Is It more complicated than it seems? o o r r r .. .. ..

Am I going about this all wrong (the wrong way) ?

Looking for guidance, and a rubber room with no sharp corners :- }}

Thanks in advance and hopefully it will help others somewhere along the way.

Thanks Again
t4him