Obtaining Tcl/Tk
Binary distributions for common platforms (discuss relative merits)
Source code
Extras you should have
Learning Tcl/Tk
Once you've got Tcl/Tk on your computer there are a number of pages that will help you learn about Tcl and Tk
Getting deeper
There are also a number of books available
Also available is the Tcl Tutor program and Online Tcl and Tk Tutorials. Alan Gauld's online tutorial "Learning to program" IS aimed at non-programmers. While the principle illustration language is Python, he also gives examples in Tcl (included with Python distributions) and Basic. See http://www.freenetpages.co.uk/hp/alan.gauld/ for the tutorial.
Web resources worth visiting include
Advanced resources