A lot of applications on the mac show a little graphic when the installer DMG is initially opened - the graphic basically allows you to drag and drop the app in that window without having to do it in finder (I'm not talking about package manager here).
Any idea if there's a standard way to create that type of experience?
Those "graphics" are just a background picture and an alias to the Applications folder.
A background image can be added to a folder by going to the view options and selecting a picture. Note that for it to work on a DMG the picture has to be located on that disk image (usually invisible)
You can also check out DMG Maker if you want some more options.
EDIT:
It appears that link no longer works. You can also use disk utility and follow this tutorial. The tutorial walks you through creating a disk image and adding your own custom background picture.
EDIT PART DEUX: There is another tutorial here