lme4 package for Mac not available
Then, try _install.packages("lme4", type="source")_. If that doesn't
work for whatever reason, you can either wait for the binary to appear or
install an earlier version.
FWIW, R-Forge has binary packages for "lme4". I've just installed mine from the command-line with
install.packages("lme4", repos="http://R-Forge.R-project.org")
and at least basic lmer() calls seem to work fine.
Best,
Stefan