Tcltk hangs when I invoke RCommander

I am a brand new user of R, running the Macintosh implementation of R.app
2.13.1 on an iMac 21" (3.06 GHz Core 2 Duo) under OS 10.6.8. I have
Administrator privileges on this machine.
Upon invoking library(Rcmdr) , I get the notice that tcltk is being called
up followed by a system prompt (>). However, the X11 window doesn't open,
and nothing at all happens. When I type any legitimate command at the
prompt, this appears in the R Console window:

*** caught bus error ***
address 0x4, cause 'non-existent physical address'

Traceback:
1: sys.parent()
2: sys.function(sys.parent())
3: formals(sys.function(sys.parent()))
4: match.arg(encoding)
5: match(match.arg(encoding), c("", "bytes", "UTF-8"))
6: textConnection("rval", "w", local = TRUE)
7: capture.output(print(args(help)))
8: paste(capture.output(print(args(help))), collapse = "")
9: gsub("\\s+", " ", paste(capture.output(print(args(help))), collapse =
""))
10: doTryCatch(return(expr), name, parentenv, handler)
11: tryCatchOne(expr, names, parentenv, handlers[[1L]])
12: tryCatchList(expr, classes, parentenv, handlers)
13: tryCatch(expr, error = function(e) {    call <- conditionCall(e)    if
(!is.null(call)) {        if (identical(call[[1L]], quote(doTryCatch)))
        call <- sys.call(-4L)        dcall <- deparse(call)[1L]
prefix <- paste("Error in", dcall, ": ")        LONG <- 75L        msg <-
conditionMessage(e)        sm <- strsplit(msg, "\n")[[1L]]        w <- 14L
+ nchar(dcall, type = "w") + nchar(sm[1L], type = "w")        if
(is.na(w))             w <- 14L + nchar(dcall, type = "b") + nchar(sm[1L],
               type = "b")        if (w > LONG)             prefix <-
paste(prefix, "\n  ", sep = "")    }    else prefix <- "Error : "    msg
<- paste(prefix, conditionMessage(e), "\n", sep = "")
.Internal(seterrmessage(msg[1L]))    if (!silent &&
identical(getOption("show.error.messages"),         TRUE)) {
cat(msg, file = stderr())        .Internal(printDeferredWarnings())    }
invisible(structure(msg, class = "try-error"))})
14: try(gsub("\\s+", " ", paste(capture.output(print(args(help))),
collapse = "")), silent = TRUE)

Possible actions:
1: abort (with core dump, if enabled)
2: normal R exit
3: exit R without saving workspace
4: exit R saving workspace



I've forwarded the entire core dump to Apple and have a copy of it but
have no idea how to make sense of it.
Odd thing is, this problem doesn't occur on my 2008 Macbook at home, which
runs the same Mac OS. It's peculiar to the iMac at my worksite. As I'm
hoping to use R in some of my advanced undergrad teaching, it'll be
helpful to solve this problem so my students can take advantage of the
RCommander GUI.

Thanks for any light you can shed on this!

--Andy Skelton

*****************************
J.A. Skelton      
Dept. of Psychology, Dickinson College
Carlisle, PA 17013-2896
E-mail: skelton at dickinson.edu
Phone: 717-245-1309
*****************************