well, ALex's link does have some of the code. We did implement it, but it doesnt look very good atm, needs some design work on how it displays.
Youll note it outputs a heck of a large picture :D and it doesnt have the thumbnails underneath, so its only partially where im trying to get to.
Not quiet sure where to edit the design, I assume it would be in the NEXTgen plugin.
The plugin is php and the code referers to checking for a nggallery.css but I dont see where that is located.
let me know if you get any closer ^^