Make some epic geometry in CoD2Radiant:
Go to Menu: Selection -> Maya Export...
Just click Ok (file will be saved in maya/bin folder in CoD2 folder)
Use the "source" command in Maya6 to import the .mel-file: source "H:\\DATA\\COD2MODDING\\SERVER\\bin\\maya\\radiant Import.mel";
The brush will be big as fuck, so that the maya camera will far-clip the geometry (and you might see nothing). Either google how to increase far-clip-range or just scale the model down to .01
For that, click ctrl-a to toggle the attribute editor and then just scale it down:
Now you got it in maya, can edit it and just export as .obj
I have no clue about textures tho, probably the dxripper would handle that.