I see. When you install Perl modules (e.g., Tk) through automated 'cpan' or "manually" by downloading, gunzip, tar xf, and then the magical incantation (perl Makefile.PL, dmake, dmake test, dmake install) they will automatically be put in the appropriate directories for your installation - with Strawberry, most likely C:\Strawberry\perl\site\lib. This way, any Perl programs you write will be able to find them.

For a separate "program" which will "use" Perl and the installed modules, you can put it anywhere you'd like. Some considerations, if it's command line, you may want the directory to be in your %PATH% environment variable. For example, I have a C:\usr\bin directory and added it to my path and it contains all the GnuWin32 tools as well as some Perl scripts I've written so when I open a cmd.exe Command Prompt, I can just type the Perl script name and it will run (you'll also need %PATHEXT% to include '.pl', but Strawberry installation generally takes care of this for you).

I also have a Perl "project" - a script with many of it's own supporting modules not on CPAN, but available at GitHub, that I put into a sub-folder of C:\usr\bin (C:\usr\bin\ppc) and then created a batch file (ppc.bat) in C:\usr\bin that points to the Perl script (C:\usr\bin\ppc\bin\ppc.pl). This to limit the amount of folders in my %PATH% variable (as I have other projects setup this way).

All of this way too much information? Maybe, but hopefully it shows you have some options and nothing says you can't change it later. So long as Perl and its CPAN modules are installed to their "default" location, things should for the most part run pretty smoothly.

Hope that helps a little more.