Adding field to check-out/billing page?

[stormysar]

I am using version 1.3.8 and am interested in adding a field to my checkout/billing page. I'd like to add a "where did you hear about us" field so I can offer referral discounts/incentives. If possible, i'd like to make this a "required" field. how would I go about doing this? I have no idea where the file is located that I need, but it's where there is a box for special instructions, plus the billing address and customer info.

[stevesh]

If you can live with it being on the Create Account page, the work's been done for you:

http://www.zen-cart.com/index.php?ma...roducts_id=186