Need the ability for my website to enter a Referral Code

We are building two E-Commerce sites using the Magento Platform. We need to add a box somewhere during the online shopping process that will allow for the customer to enter a referral number. This promo number is not for a discount on the merchandise... rather it will be used to track the sale of the merchandise and feed to a report that will let us know which salesman referred this customer and give us details of the actual transaction. If you think you can provide us with the functionality for our sites, please contact us immediately. We are looking to have this project completed no later than July 27th. Thanks so much! Heath