Excel 2007 : Auto-Fill/Validation help!

Hello Excel Forum!

I am currently working on a project that I would like to limit the number of entries in a column. For instance, I have cells C10 and C11 that I'm working with. Both cells CAN be a value of 3, or 0. BUT only one can be a 3. Both could potentially be a 0.

I've tried the Data Validation to limit it so only one can have a value in it, but it wouldn't work for me when I put a 3 in C10 first, it would allow me to put a value in C11. If I put a 3 in C11 first, then it would not allow me to put any value in C10. This was odd.

For the rest of my workbook, I am wanting to limit the amount of entries as well, but the numbers differ. For instance, C15-C18 are point values of 15, 13, 11, and 0, respectively. Those ones, I'd just like to make it so individuals using this cannot enter more than one value in that group of cells and once a value is entered, the other cells change to a "-" or a "0"

Any suggestions or easier ways to go about this?

See attached sample.

I don't quite follow, I've been trying to play with it for a bit now. Here is an outline of my spreadsheet.
Ratings - Book1.xlsx