I have problems with a really slow ftp speed so I used the following (I use a laptop for everything so mobility to connect my HDD is no problems)
Connect your external drive to the pc and formt it to fat32 using programs like swissknife or the really easy guiformat. Create a folder called games.
Use xbox backup creator for extraction of ISO. Open it and go to Image Files tab. Hit Image browser, then File; Open image file and select your ISO from the browser. Simply right click on the root of the file in the left panel and select extract. Browse to your RGH HDD to the folder games that you have created and make a new folder with the name of the game.
Allow it to extract for a few minutes (or seconds for kids kinect titles) and you're done.
Make sure your FSD paths are set to that folder and it will appear in games list.