$ compiz-manager decoration move resize
That will start compiz and run emerald as the decorator.
Edit: It could just be that compiz starts, fails and bails at the moment explaining what you're seeing. Try the command above ...
]]>I believe compiz-fusion is a package group containing all compiz-related packages.
Aha! no wonder I couldn't find it in the packages repo. meta packages should also be shown on the package database link, IMO.
]]>$sudo pacman -S compiz-fusion