Can't start R

[YO Katsuyasu]

I am trying to use R on ESS. However ESS doesn't work well.
When I try to start R on emacs (M-x R), ESS responds error;
"Searching for program: no such file or directory, R"

Does anybody know why I can't start and what I should do to start R on 
ESS?

R runs normally on terminal programs like xterm.
I use MacOSX, Apple's X11Beta3.
Emacs21.3.1 and R1.6.1 are installed by using Fink.
ESS-5.1.24/ is manually copied to my site-lisp directory.
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YO.K
yo at kais.kyoto-u.ac.jp
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