license-mix, legal consequences?

[Henningsen]

I want to release code I write myself under a dual license scheme, both GPL
and commercial license, the latter for people who want to use the code in
closed source projects. In my project I would like to include code released
under the Tcl/Tk license model ("keep copyright notices in place, and keep
this license text with the code"), and code released under the MIT license. 

I checked on the FSF's site whether these licenses are compatible with the
GPL, and didn't find anything. Are they or are they not? And if they're not,
would that mean that people who want to use my GPL-released code could not
also use the code modules with incompatible licenses unless they got a
special permission from me (in effect a free commercial license)?

Peter Henningsen
alifegames.com