Download for Xbox must be on internal drive !

Crud, haven't added internal memory to my Xbox and have the old 4 GB slim.. it was a gift so couldn't say anything. Have a 32 and 16 gig attached and was going to add internal memory at a cost of 129 bucks before game release in Sept. Found out I can't download Beta to an external drive, which sucks. I pre-ordered for PS3 and my Xbox 360, but planning on playing on the Xbox since my normal band of gamer friends play Xbox plus we can use the party chat...So...I have to wait till end of month to afford the internal add on, so damn it I can't play the Xbox Beta version...Guitarmama's wings have been clipped..oh the humanity !!! If you have friends who can't download and getting black screen on Xbox and using external added memory drives, let 'em know would ya???