Many years ago, Microsoft wrote an article on how to drag and drop in Access 95, 97, 2000 and 2002. Then Doug Steele improved on that in an article for Smart Access in 2004. I have just tested the code in Access 2007 format and it works fine. If you like a bit of a coding challenge, the Access 2007 download and the samples are available here.
In the following diagram, you will see what happens when you select multiple entries from a List box and drag it to a Text box. Its pretty neat really. Well done Doug.