Brion-
The following commands must be available in the default execution path (PATH environment variable):
latex dvips convert gs
and anything else that they depend on that I might not know about. In particular ask that dvips is installed, since you didn't mention that earlier.
And as I just found out through two hours of pain, GhostScript in certain versions doesn't work with ImageMagick at all. See this bug report: http://ghostscript.com/pipermail/bug-gs/2002-July/001451.html I used an older version (8.0 something) and it still didn't work. Only going back to 7.05 did the trick.
One thing that helps in debugging is to edit render.ml in math/, remove the "/dev/null" redirections, recompile and test on the commandline according to the README. Then you should see exactly what goes wrong where.
texvc is really quite terrible when it comes to error messages.
Regards,
Erik