Halo 1 on a macbook air

hey guys. i'm going to new york soon, and will be on a bus for a while, so i want some entertainment.

i have the most recent macbook air model, 13"

i want to get halo combat evolved on it, but its a little more challenging that you'd think. I've only found 1 torrent, and that only works on snow leopard (im fully updated on ML)

on amazon, the mac version is $35 used, and i can't find anything better on ebay.

does anybody know anywhere i can get it for cheaper? (maybe have one you want to sell)

also, is the only way i can install it is by using an external dvd drive, or is there any way to put it on a flash drive (on a different computer) and install the image to the mac properly?

thanks!