I am very bored of the default themes in Ubuntu, not because they are bad just because I get bored easily!

I decided to visit Gnome's Theme library and found a theme I like. I downloaded the theme and tried to use the install feature in the theme panel. As soon as I click okay after finding the theme package my system freezes.

I decided to try the other way and selected open with (Theme installer) which did exactly the same thing.

Is there a terminal command to install themes or a way to reset the theme manager?
I am using Natty and Gnome 2.32.1