I had been trying unsuccessfully for several days to install Darcs via MacPorts and Fink, but both seem to have trouble with the prerequisite GHC on OS X 10.5 (Leopard). However, I did find a very nice installer package for Darcs here that worked like a charm for me.
My new MacBook Pro arrived yesterday. I expected that it was going to come with Leopard pre-installed, but instead it came with Tiger and a Leopard DVD. Perhaps this is better in case there are enough bugs and incompatibilities, that I’d rather use Tiger until Leopard matures a bit. I have installed Leopard and haven’t played with any of the new features like Spaces or Time Machine, but I have run into a minor problem or two with X11.app.