This seems to be a pretty common feature in most Windows-based IM clients and I'm confused as to why I can't find this functionality in Adium. By "dock" I mean dragging the buddy list to the edge of the screen and having it essentially turn into a sidebar which no windows overlap and which takes up the entire height of the screen.
You can certainly achieve "something similar" if you tell it to be above other windows and don't hide when in the background (options I don't use or like)
Of course it won't be a real "docked" app like the DOCK, but it will behave mostly like it.
You can control the vertical and horizontal size:
And here's how mine looks:
UPDATE to be honest, I use it on the right side, but Adium will "stick" to the Screen side when close to it. The position in the above screenshot was for the purpose of showing you how it "docks" :)