About D2D for those new to it.

You can download your games unlimited times from the Direct2Drive server. Unlike steam, the games aren't tied into a client- the CD keys are listed under your account on the D2D website and are needed upon activating the game for the first time only.

You can install any game on an unlimited amount of computers. Some companies however may have other DRM specific rules not unique to this. (Chronicles of Riddick allows only three installs).

You are basically downloading the ISO or Disc Image of the game. You have the option to back up the game on a DVD.

You do not need to be online to play. Activation is done online however. You activate via the phone if internet is not available.

A separate, unique, key is given to you additionally for multi-player games - this is your multi-player key.