I still can't get HG to build with MacPorts/SnowLeopard ... seems to be a problem with Python.
If you're intent on building from source, make sure you're running "sudo python setup.py install; sudo make install-doc". Installing with the makefile directly will place packages in /usr/local, where Python doesn't normally live under OS X.
For reference, mine is:
/usr/local/lib/python2.6/site-packages/:/System/Library/Frameworks/Python.framework/Versions/Current/lib/: