levelgeometry is definitely not the right way to model a helix in gs (or any other bsp render engine). the only reasonable result can be somthing like this:
(if this is what you are looking for contact me via mail and i will send it to you)
everything else more round or complicated is veeeery hard to create. you should use a mdl instead. either in med or other model editors like milkshape, blender aso.
cheers