Halo 2: big beetle thing

Last night, on the day before Halo 3 was released, I remembered that I've never completed Halo 2's singleplayer mode. In fact, as it turns out, I've hardly started it. Having to start afresh on my Xbox 360, it was pretty engaging and I played for an hour and a half, passing where I'd previously reached - landing on Earth, and working my way around the coast to a bridge. I think I'd reached the bridge before, but had never crossed it in the tank, nor chased the scarab down. I keep on finding myself running out of ammunition, which is a pain, but just before I saved and quit I found a massive bunch of guns. I'm expecting a bit of a rampage now ...