I found (in the german www.level-designer.de forum) a tool that will create a spiral staircase. like this:
(pic is also from the forum)
the tool is still in beta status … so check it out. I will send comments and suggestion to “JakeTheFake” who coded this little tool.
DOWNLOAD
btw. the tool support the CoD.map format too.
(at the end of the month the link can be down for a few day… he`s changing his webspace)
greetz
ok, i have suggested this to him. i have made a translation by my own (with PS :)) i hope its understandable (corrections are welcome)
greetz
btw. “z-offset” is a new feature
minor suggestions:
stephigh = step height
stairhigh = stair height
coresize = core diameter
Caulk Textur = Caulk Texture
avoid to combine two nouns to create one new noun… usually the nouns stay seperated in english
but on the other hand… all my comments are pure nit picking… and: my english isn’t the best, so maybe it’s me who is wrong… so… “nix für ungut” 
thank you. ! I was baffled by the language barrier…I had to keep trying until I got close to what I needed.—Now I can just get 'er done.