I upgraded my video card driver once again using the directions here (using the most modern driver), and Second Life stopped sucking! That makes me happy.
I was so bummed about my Second Life experience, I had contemplated getting a Mac. Unfortunately, the Macbook (non-pro) doesn't work with Second Life, and the Macbook Pro is like a grand more--i.e. way more than my wife would ever let me spend.
Anyway, I'm happy.
(Dell Inspiron 6400, Ubuntu 6.10, ATI Mobility Radeon X1300)