i think there are some freeware paint style programs out there.
the design was really hard. its sorta based on the spacecraft from the start of Avatar, crossed with a space station and some ship from a docu-drama i saw once about a group of astronauts flying round the solar system. their ship had a big shield on the front to serve as an air-break in Jupiter atmosphere (or something like that) after a bit of trial and error i got the basic shape done. the extra details, like the scaffolding, came after and took a lot longer (did a lot of copy and paste to keep it all regular.)
Very nice. I think I remember the docu-drama that you're talking about.
You can definitely tell that you put a great deal of time and effort into designing that ship.