This is how gitk - which is based on TK/wish - looks on my fresh 11.04 installation:
Are there any better fonts that TK/wish can use by default?
You can install tk8.5
and then update wish alternative:
$ sudo apt-get install tk8.5
$ sudo update-alternatives --config wish
Be sure to select /usr/bin/wish8.5
.
That should do it.
Good luck