Thanks a lot, you're explantation has really shed some new light on the problem for me.
Unfortunately, english is richer than french on that particular subject, the "-ever" part of words like whatever, wherever, etc doesn't exist in french, that's part of my problem. We only have quiconque/quelconque for whoever/whatever and all the rest is rendered by words order and the subjonctive tense (wherever= où que ce soit/où qu'il soit for exemple)
Another problem is that in french textbooks you learn that никто=nobody, ничего=nothing, нигде=nowhere, etc and that ни....ни (neither...nor) is also ni...ni in french, so basically you only learn that ни is "no" or something negative and that's all. Your exemples with что-НИбудь is really telling me something else on that aspect.