Well, the arcueid binary expects to find arc.arc in /usr/local/share/arcueid, and like I said there's practically no error handling. You can either do a make install (which should copy arc.arc to that place where the arc binary can find it), or you can run it as src/arcueid arc/arc.arc (explicitly specifying the path to arc.arc on the command line). Oh, and do a git pull!
You don't, at least not for now. I found it faster to just write a version of the compiler in C using compiler.arc as a prototype (the fact that I've done this should be obvious by comparing compiler.c and compiler.arc). Seems there are a few more bugs in the compiler: the or macro seems to be expanding all wrong, and anything but nil crashes it. I need to take a closer look.