Thanks for the tips, BnM, with those steps I came in and beat the crap out of it on the first try. I think my problem was less-than-optimal portal placement.
I then went on to beat the rest of the levels. Fun time! Bill, I watched that video, and now I'm seriously going to have to try to pick up the Orange Box. I have a MacBook Pro with a pretty decent video card, so rrunning it (w/ Parallels) shouldn't be a problem...