infopath 2003 had this option, I do not think infopath 2007 has this. I think it was called an option box or something. it gave you the ability to select from the list and if not there, type it in. However if you want that value to be there with the next form that is open, you will need to capture it either in an xml file or database, and have that drop down list box pull from that data source.