Here is a good guide for setting up the shell environment for MacPorts:
http://wiki.inkscape.org/wiki/index.php/CompilingMacOsX#Setting_the_build_environment
There seem to be a lot of people who use Mac OS, but are having trouble compiling unnks. If you publish a user-friendly graphical front-end for unnks I'm sure it will be very useful.
Can you see if there is anything explaining the failure in config.log file after doing ./configure?
If libgcrypt is installed but it can't find it, then maybe your environment is not set up correctly. Maybe you are missing "-L/opt/local/lib" in your LDFLAGS, and "-I/opt/local/include" in CFLAGS. There should be a script that comes with MacPorts that sets all of this up.
