Hi
I am also new in OMNET so my answer might be inefficient but it works
to run examples in omnet you can use the windows console preparred in OMNET (I mean omnet/mingwenv)
Run it and cd to the "Simulations" folder and the project you want to run and then type run
the example will run in the normal GUI form.
As you see each project has only an ini file.
you can also develop new projects by setting up of new seeting in an ini file (and of course using of existing modules)
if you need to modify a certain module e.g. a node, copy and paste one node model and modify it.
however it is not still clear to me how to change the network topology more than the mentioned method.
Behy