My system is: debian6 + r-2.15.
I have installed tcl-devel and tk-devel with apt-get:
apt-get install tcl8.5-
I think you are doing this wrong.
Read the README at http://cran.r-project.org/bin/linux/debian/ to learn how to get the current R version for your Debian version (be it stable or testing). This version already has support for the tcltk package which comes with R, provided R is built the right way. Which is easiest to assure with a proper pre-built version.
You can check that by looking at capabilities():
R> capabilities()["tcltk"]
tcltk
TRUE
R>