Walls and Ceilings - Putting up drywall, kind of in a pickle

I am finally getting around to doing the back wall of my garage where it looks like the previous owner had some work done to the pipes and just threw up piece of drywall to cover it up.
http://i2.photobucket.com/albums/y44/fox_forma/New%20house/Picture013.jpg

I pulled off all drywall to the left and really don't want to do the entire back wall and have to take down everything. I would like to know where I need to transition the drywall so it lined up the best has the best chance of staying even with the remaining wall up already. Right now the wall that is still up is basically dead center of a 2x6 for most of it. I figured I would stack two 4x8 sheets of drywall horizontally when installing the drywall but to do that I would need to take down more wall and I will be in the middle of a 2x6 if that makes sense? How would I support the drywall that goes past the 2x6? I have a few more questions as well but will hold off for now. This is what I am working with as well.
http://i2.photobucket.com/albums/y44/fox_forma/House%20projects/Picture138.jpg

http://i2.photobucket.com/albums/y44/fox_forma/House%20projects/Picture146.jpg

Thanks

Hope I understand correctly. You can cut the length of the 8' sheet of sheetrock so it fits against the good installed rock and so it sticks behind the 2x6 wall attaching it to the nearest the wall intersection. If you are installing rock on the short 2x6 wall, just cut it to fit and screw it to the wall members. You are close enough to the corner so you won't need a stud directly in the corner. You can tape the joints and it will be fine. Let us know if I misunderstood what you were doing.

You are correct in what I am getting at, I just wanted to make sure I could do it that way. The sheet rock still up is for the most part centered in the 2x6 but I also was just looking at it again and there are a few spots that it looks like I might have to come in on an angle with a screw to secure it again.

I actually just took out the corner you see the framing for. The previous owner put it up for a wall switch but I am moving that and getting rid of the outlet that was in that little section and putting a door back up to the outside. I am sure there will be gaps where the two sheet rock pieces meet since it isn't a perfectly straight line cut through the remain sheet rock hanging. Any tips on how to fill that in? Just pack it with mud or is there a better way?

Off to get some stuff at lowe's.

Thanks for the response Chandler, you are always a help Beer 4U2

Where the drain lines go through the studs protect them so you don't put a screw into the drain line.

Thanks for the tip but the line are deep enough back that a screw wont get it but I will watch for that as well. One thing I am concerned with is where the pipes go into the foundation they aren't flush or inside the framing, they seem to still out just a hair which would cause the dry wall to not sit exactly flush to the wood all the way across.