I was wondering if I could change the built in horizontal menu which is used in thethememachine to Vertical in aside first instead of navigation.

Any hint to where I should find the script or css would be helpful.

Thanks

I'm not sure how difficult it is but have you considered using a free menu module that supports this?

Here's a good one.

http://gallery.orchardproject.net/List/Modules/Orchard.Module.Szmyd.Orchard.Modules.Menu