Yes installing the Microsoft Core Fonts did the job. Here's a quick how to for other people that may be experiencing this in Ubuntu 8.10.
Non-Terminal:
Go to Applications > Add/Remove...
and...

* -1
The square root of -1 is -1 we say. So it would just make your number negative.
Maybe this documentation is helpful for you too :)
http://en.wikipedia.org/wiki/Complex_number