Mandatory One Attribute Or Another

Dear Folks,

I have developed a shopping cart for selling artwork.
During purchase use can either purchase a poster with varying sizes

8 x 10 Poster
10 x 12 Poster

OR

they can purchase the artwork on canvas.

12 x 14 Canvas
14 x 18 Canvas

We have a plethora of other products that don't have anything to do with canvas and poster. Anyway to put in a client side OR server side check
that the customer selected either Poster OR Canvas and not both.

Regards,

J

Option Name: Poster or Canvas Artwork Dropdown list

Option Value: Please select Artwork 0
8 x 10 Poster 10
10 x 12 Poster 20
12 x 14 Canvas 30
14 x 18 Canvas 40

Attribute Controller:

you need to add flag properties to Please select Artwork 0

1. Under Attribute Flags: the colored boxes
2. Yellow box, Used for Display purpose only: Click Yes
3. Tan box, Default Attribute to be marked selected: Click Yes
4. What this does is force a customer to click their sizes correctly
5. Right now I can add to the cart and not select a size or color.. BAD
6. The beauty of this is a warning box appears at the top of the page and states they have not selected the attributes you offer to a customer.
7. 8 x 10 Poster 10
   10 x 12 Poster 20
   12 x 14 Canvas 30
   14 x 18 Canvas 40