You get Shadowrun Fever by teabagging someone who already has the achievement... such as myself :P

Shadowrun is a great game!  The boyfriend and I rented it the day it became available and we already bought a copy so we could both play as one of us was always sick of watching! 

There are two different tiers of Xbox Live.  There's the free Silver subscription and the $50 per year Gold subscription.

 The Silver subscription gives you access to the Marketplace where you can download trailers for games and movies, free and premium content for games, free and premium gamer pictures and themes and many other items.  It also gives you access to game updates as they are made available, and the ability to have a friends list - a list of 100 people that you can text, voice and/or picture message (with the Vision Cam).

 The Gold subscription is what allows you to play online multiplayer with other people over Xbox Live.   If this is what you are wanting with Xbox Live then you are going to need an Xbox Live Gold subscription, which can be bought in-store, or from the console itself (using a major credit card).