I have installed Tk in strawberry 5.12.0.1 recently and didn't fined any problem.
Try manual installation if CPAN install fails. Try following:
1. Download tar.gz file
2. Extract using Winzip or 7zip
3. go to the folder "Tk-804.028_503" in command prompt
4. type: dmake
5. type: dmake test
5. type: dmake install
In my case Tk test failed. u can skip that and install directly