Oskar
Dia is certainly the type of tool you are looking for. It is for the
same reason that I became interested in it also. However, Dia is still
in an early stage and the range of objects available is still limited.
If you have a little C programming experience you might consider working
on some flowchart objects. It's really not too hard and you'll soon get
the hang of it.
There are other drawing tools but I haven't seen anything quite like Dia
yet. But if you're looking to get work done quickly you'd probably be
better trying something else instead. Something simple like XFig can be
surprisingly effective once you get used to it.
-Rob
PS: Oskar -- I'm just around the corner in the Architecture faculty if
you want to get together for a chat about Dia. I'll happily give you
some hints about how to get started developing new objects.