You can use this module with the following in your ~/.xmonad/xmonad.hs:
import XMonad.Layout.IM
import Data.Ratio ((%))
Then edit your layoutHook by adding IM modifier to layout which you prefer
for managing your chat windows (Grid in this example, another useful choice
to consider is Tabbed layout).
myLayouts = withIM (1%7) (ClassName "Tkabber") Grid ||| Full ||| etc..
main = xmonad defaultConfig { layoutHook = myLayouts }
Here 1%7 is the part of the screen which your roster will occupy,
ClassName "Tkabber" tells xmonad which window is actually your roster.
Screenshot: http://haskell.org/haskellwiki/Image:Xmonad-layout-im.png
For more detailed instructions on editing the layoutHook see:
XMonad.Doc.Extending
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