I had the hardest time finding this information, as it was collected across many forums from all over the place, so I've put them together for future reference, and hopefully assist anyone struggling with a similar issue.

Assuming your regular Airport Extreme setup went off without a hitch, here is how to get maximum use out of your Boxee, and Airport Extreme when drawing from the same source external hard drive, simultaneously.

What I'm working with: Iomega 2TB HD, Boxee Box, Airport Extreme, Mac Air

Mac Instructions:
- Open Airport Utility.
- Double-click your Airport Extreme icon @ top left of window.
- Click on Disks.
- Click on File Sharing Column.
- In Airport Disks Guest Access pull down menuSelect READ ONLY.

Boxee Instructions:
- Go to Settings.
- Select 'File Sources'.
- Highlight & select 'Add Sources'.
- Scroll down and select 'Windows Network (SMB)'.
- Select your hard drive from the list.
- Select 'Add this directory' for the folder(s) you wish to use via the Boxee.
- Check applicable Media Type, & type of scanning you prefer.
- Click ADD

Return to the HOME menu on Boxee and source the files/folders you wish to play, as you normally would have with a wired connection.

The final success test for me is playing music in iTunes without wires AND watching a video via Boxee on my TV pulling the music & tunes from the same hard drive. Again, not having to pull out this USB cord and switch it with that one is incredible. No frustration with this & getting what you pay for = wicked! Have to say, works great, no slag in the video or music playing.