Because you may already have the dependencies on your system, here's another way you can find out what you need.
Install just the R-2.9.1-i586-1vl60.tlz package using installpkg, as previously noted. After you install the package, run
as root from a command line. Then run R from a command line. If it starts up and runs fine, you're all set and do not need to install dependencies. If you get an error message complaining about a missing file, note the name of the missing file (usually something from /usr/lib) and see if you can download it from the repos just as you did the main package. Install the dependency and try again. When you stop getting complaints and the program starts and runs, you're done.
This can be tedious when you don't have an active Internet connection on your system. However, it sure beats downloading bunches of packages you may already have.