I got it to upgrade. I guess there is an order to how I built my machine. I started with a clean install of 10.5.2, got all my drivers installed, then ran all the updates except for the 10.5.5. update. Then ran that update, and it worked. I was using a patched package that I had saved previously, and it was probably the culprit.

We should probably make a sticky of nfoav8or's post with the "pre-patched" updates though. That's good stuff to have.

Thanks for your help! Forums like this make everything easier!