How can I check for variances in spelling within form text input fields?

Hi, I would like some ideas on how to perform the following. Any input from the PHP gurus would be appreciated. I have a form where my customer feels out certain information. Part of this information is the company name, address, city and state/province of their customer. I have to assign a unique number to their customer based on the information they typed in. Here is my problem: 1) They may enter the same customer twice but have a slightly different spelling (maybe adding a LTD. to the company name) 2) Two of my customers may have the same customer. They will type it into my form but again with variant spelling. I would like to know if there is an algorithm which allows me to check for small variances in spelling so that I would know if this customer has already been assigned my unique number and therefore not assign a duplicate number. Thanks, Don