Nordic characters mess up post slugs

It seems that WP won’t handle special characters correctly in the slug – and this causes some problems. Is there some way to fix this, for instance making WP replace the characters in the slug?

With Norwegian bloggers this happens with ? / ? / ? (ae/o with strikethrough/a with ring). Use it in a title, and the slug (and the page’s link) becomes a mess – sometimes not even recognizable.

I’ve just installed the great SimplePress forum, but because of this failure (which I believe is connected with WP itself), no forum posts with ?/?/? can be opened. I can avoid using those characters myself, but not stop my forum users from doing so.

Some workaround, plugin or idea to fix this?
I know they have similar problems in Iceland, Russia, Sweden,… – places with more characters those included in “proper English”.

Thanks a lot for any suggestions

Kjetil