Games for Windows LIVE DLC DRM?

I know there are no add-ons for any GFW-L game yet, but does anyone know if it will pull a 360?What I mean is this: When I download something to the 360, anyone can use it. When I download that same something (or move the storage device) to another 360, I (my gamertag) have to be signed in to LIVE. I am asking if the PC will behave in a similar manner.The reason I'm asking is because my bro and I each have our own computers, and only one copy of Fallout 3 (currently installed to my computer). The LIVE key is already being used on my account, so he'll probably have to make one for offline use. How would he be able to access the DLC in this case?Also, since I already used the LIVE key on my account, can I use it again on my bro's gamertag?