Installing Tcl 8.6.4 on Windows :
The easiest way to get Tcl on a windows machine is to install the ActiveTcl distribution from ActiveState.
Navigate to www.activestate.com and follow the links to download the Free Community Edition of ActiveTcl for Windows (choose 32/64 bit version appropriately).
Run the installer which will result in a fresh install of ActiveTcl usually in the C:\Tcl directory.
Open a command prompt to test the install, type in "tclsh" which should open an interactive tcl console. Enter "info patchlevel" to check the version of tcl that was installed and it should display an output of the form "8.6.x" depending on the edition of ActiveTcl that has been downloaded.
C:\>tclsh % info patchlevel 8.6.4