Thanks for the reply, and good guess! I've updated my original post to explain a bit more about what I'm trying to do.
I like your idea, but note one thing about your solution -- it compares lines to eachother twice. When it's on line 1, it compares to line 2, and when it's on line 2, it compares to line 1 (even though it already has). That's why tye's combinations sub is really nice, it cleanly eliminates that problem. I'm not sure if using combinations is faster or slower (intuition tells me it would be faster, since it's comparing less, but perhaps there's some overhead getting in the way), but the duplication was driving me crazy.