Search as you type

Hi there,
I would like to define a custom field, likely as a simple text field, in which I would like to hook a function into that searches for all authors (or users) of my wordpress site. So when the person starts to type 'sas' it will find and show all authors (or users) beginning with the letters 'sas' to choose from. I have seen this in a plugin 'co-authors-plus' and some of the code for it is here: http://pastie.org/2450672
Is there a way to get this working with GF? Sorry, but I am not a great coder to work this out myself. But if you give me a starting point which hooks/filters to use then maybe that might get me on the right track...