You need to install the drivers for your graphics card. I'm assuming your on windows, so it'll be as simple as running a installer and rebooting.
Does this: /home/spencer/.tremulous/base
Look like Windows to you?
I expected more from you, David.
Now, seeing as how I don't have a Linux, I have no clue what I'm looking for, but
this site looks to be what you need. In the first column, choose "Graphics Card". In the second, choose what kind. And in the third, choose one of the Linuxs. Then click go, which is below the bottom left corner of the first column.
Hope this helps, sorry if it doesn't.
EDIT: Okay, it may or may not be of help. I have no idea what the different versions of Linux are like.