[safisher]

I've ran several campaigns using all sorts of CoC products. Beyond the Mountains of Madness and Walker in the Wastes were both excellent adventures for my pulp GURPS approach. All you really need to do is get GURPS Horror 4e, as it is written by Ken Hite, and he knows Cthulhu very well. All the atmospheric and psychological elements of CoC are in Horror as well a templates for Cthulu-type monsters, magic, and so forth. Can't recommend it in enough. GURPS Cthulupunk is good if you want the specific future setting, but I don't think you need it in addition to GURPS Horror.