Software advise needed

Hi all!

Hope you don't mind me asking the following question (I had no time
reading through the archives yet):

I need to draw a sketch of a music instrument, that I want to get
build (me in Germany, Starrlabs in San Diego/USA). An easy software
is needed on a not much more than one-time-only basis that allows me
to draw lines & circles and shows me the exact length I am drawing in
cm/mm or (less good) inch. Cool would be to be able to write numbers
into the sketch to have the length/size written down in the drawing
as well (like one usually does on real paper). Is there such a
program available as Freeware, that allows me to save the "picture"
as jpeg or pdf. file? Do I need a special hardware drwaing tool for
doing this (you know: a wireless pencil or something?)?

Best would be a program that allows me to take a photopgraphy found
on the webpage of Starrlabs and translates the "seen" dimensions into
more large & more dimensional, allows me to circle the view and to do
a cut & paste job (cutting a joystick here, putting it there), but I
believe this is just wishful thinking...

Thanks a lot in advance for any help

Harry