I'm getting Fallout New Vegas Ultimate Edition for xbox 360 & I wanted to know if i could share my DLC disc with my friend on his xbox 360 & still be able to use it on my own. & does Fallout 3 GOTY Editon work the same way?
Yes. You can copy it as many times as you like, and its quick and easy.
That'd the benefit of actually OWNING the game, and not getting caught up in DRM schemes that merely give you a license to play.
In other words, never -download- DLC as you don't own it (read the terms of service) - ALWAYS wait for the retail versions or GOTY Editions and all that.