DropDownList and applying a wildcard search w/n a stored proc to that ddl

Hi - I have a quick and easy question: I'm trying to put a stored procedure that has a wildcard search associated with it. The proc is going to be based off of an input selection from one of my other dropdown lists (my company list) and then a wild card lookup on its own list. If there are 4 or more char then it does the wild card lookup -- if its less then 4 its an exact match. Can anyone tell me how do i go abt applying this to the ddl. Thanks, Ryan ...