Make a text attribute required ONLY IF another attribute is set

Client has a product where a portion of the sale goes to a charity. To cater to this, I have a Charity attribute that uses the drop down attribute type and it has these options:

1. Destination A
2. Destination B
3. Donate to a specific school

If the customer chooses #3, donate to a specific school, then we need to know the name of the school to donate to. To collect that information, I have another attribute field called, SchoolName. SchoolName MUST be filled-in if Charity is #3. Otherwise, SchoolName can be left blank.

My question: how do I make the SchoolName attribute required, or not required, based on the value of the Charity attribute?

Bonus points awarded if you can also show me how to make the SchoolName field only appear if Charity choice is #3.

Thanks in advance for any help provided!

You might try the Improved Attributes Controller.

Hope this helps.