For those who have had trouble installing "Starved for help" try this and everything should work okay.
Open the game and you will get a message to return to the telltale website to download an update.
Go to your account and choose the Mac icon from the "your purchases" section next tot the walking dead. This is not the second episode, just a vital update. It's about 550MB.
Then once this is done install the game by dragging it from the disk image to the applications folder.
Open the game and now go to Downloadable Content. Episode 2 "Starved for help" should have the word "Get" next to it, click on "Get"
You will now download from inside the game. Do not break connection as it starts again (I found that out at 73%, nice)
Anyway, hope this helps.