Question about downloading XBLA Games

Hey guys, I just got a 360 a few days ago and I have a couple of questions. First, since I don't have the wireless adapter yet, and Auburn University took all the landlines out of their dorms, my Xbox remains disconnected from the rest of the world, but I really want to download Portal: Still Alive but have no way of doing it, so would it be possible to download the game on my computer then transfer it to the xbox?

And nextly, is there a cheaper alternative to the $100 Wireless-N adapter from Microsoft?

you can buy the orange box, since it has portal, half life 2, and its two episodes and team fortress 2, its only 20 bucks.

You can get the old wireless adapter, i think it cost 60 bucks now

I have the Orange Box, but doesn't Still Alive have additional maps?

And I'd rather have Wireless-N.