Well, it's on the git now. To have the executable, just run
mzc --exe arc1 arc1.scm
If you feel adventurous, mzc --gui-exe arc1 arc1.scm might give you access to MrEd, the graphical library of MzScheme (a MrEd binding to arc could be a nice thing :) but I didn't try it.
Very nice. Both your suggested commands worked for me (on Windows XP).
I like the GUI especially (it actually solves a bug I found with mzscheme that was stopping me from pasting code directly into the command line). Although I find it somewhat strange that I have to click quit twice in order to actually close the program.