While I don't have Windows 7, this looks like the same behaviour as Windows XP.

If you use the commandline (something like C:\> perl tk_scriptname) you won't get the extra window. You'll find this useful for debugging when developing your Tk applications because that extra window will disappear when the Tk app finishes and you won't get any feedback if something goes awry.

When everything works the way you want, the only way I know of to run (via double-click) without that extra window is to compile your script. I use pp for this under Windows XP. The -gui option gets rid of the extra window; there's also an -icon option if you want a custom icon for your Tk app. Note: the executable created can be quite large: a script of a few kilobytes becomes an exe of a few megabytes.