For Aqua, you will need to use the macosx version of TCL/TK. TCL seems to be included as part of the Developer tools package, but not TK, so most likely you will need to install your own version of TCL/TK 8.4.2 (or higher).
Go to the macosx subdirectory of the TCL/TK distributions. Type
make install INSTALL_ROOT=$HOMEThis builds a framework library and installs it into
~/Library/Frameworks. You could also install it
system wide with make install, but you will need administrator
priveleges for this. Eco Lab will search either place for the TCL/TK
libraries.