How to make multiple fields required based on a Check Box selection

How to make multiple fields required based on a Check Box selection

I'm creating a credit application form asking the user to check off customers he wants to open accounts with.  I created a list of Check boxes for each customer (30+ check boxes).  If the user checks off a certain customers, how do to I make other fields on the form required?

Example:
Check Boxes for.... (user can check off as many accounts he wants to have opened)
- Flooring: ABC Carpet
- Office:  Office Depot
- Paint: Our Paint Co
- Flooring: Your Floor
etc...

If they select a flooring supplier (they are all named to start with "Flooring"), I need to have certain fields on the credit form become required such as...
- Tax ID
- Trade References #1
- Trade References #2
- Bank Info #1
- Bank Info #2