I finally fixed the header on gumaxv and its working with mediawiki 1.18 and wikieditor extension is also working.
I had to copy the UsabilityInitiative.php into the extensions folder before it could work.
Here's a screenshot

Ok now that i've been using my wiki with gumaxv for a few days, I finally came across a problem. The wikieditor extension doesn't seem to work on this skin but it did with gumax 3.4.5 Paul do you know what could be the problem here? I don't see myself going away from gumaxv. i have a test mediawiki ...

I adopted mediawiki for a project i'm working on and I startd working on it in nov 2011 so i'm not an expert on mediawiki or php coding. I wanted the vertical menu skin on mediawiki that's why I was using GuMaxV until two days ago when I upgraded my mediawiki to 1.18.1 from 1.16.4. Disaster happened...