Greetings!
Things are a bit
slow at the office today. Well, technically I could be doing something useful, but I actually started looking this up (origin of the letter w). Suffice it to say, most links I found seem to point to it being used as literally a "double u", and that it got mashed around a bit over time.
I will spare the links to the sites about the Phoenician alphabet evolving into "upsilon", etc... This is left as an excercise for the bored reader. See
Google: letter origin w.