OK, here goes. The code is on Pastebin: http://pastebin.com/nF5pqtzR
You need to download the galleryview (http://spaceforaname.com/galleryview) and fancybox (http://fancybox.net/) jQuery plugins.
You will see the code to include those scripts in child_add_styles_and_scripts() so modify it accordingly.
You should be able to paste all the code into your functions.php.
The supplied code DOES NOT include any CSS since it's all in one file on our site but you should make sure the CSS for the fancybox and gallery view is included. You can use the child_add_styles_and_scripts() function to add the CSS.
To insert a gallery into a page or post, just upload some images to a post/page and use the Insert Gallery button. You don't need to specify any parameters except the ordering. The others are ignored for obvious reasons :).
This code may not work straight off the bat as I haven't tested it like this. I have pretty much 'ripped' it out of the site with minor modifications. However, you should be able to make it work - just make sure the JS is getting loaded where it should and that you have the CSS loaded as well.