AutoCAD is a professional drafting tool for (mainly) 2D design.  Dont bother trying to design the cab in a paint package (Photoshop, Paintshop Pro etc) as they just arent up to it (IMO).
I used AutoCAD 2004 to re-draft my UAII plans and make minor modifications.  However such a program will require a certain amount of time to 'get to grips' with (as will most applications).  Luckily I had a job as a trainee CAD technician, working in a drafting office...so had a head start.
Unless you can 'source' a copy of AutoCAD (it's expensive if you're buying), then you may be better off with a cheaper alternative.  Anyone make any suggestions?
Craig