I think my problem is trying to get the ESC to arm. From what I've heard I need to start it out with 1000 us pulses for a couple of seconds, which I've tried and haven't had any luck. This weekend I'm going to see if I can use the arduino to sniff the signal the radio receiver sends the ESC and then try to replicate that.
ESC safeties tend to take a specific pattern to unlock. Try a couple seconds of 1000 uS, followed by a couple seconds of 2000 us, followed by 1000 uS. You should now be "armed." If that doesn't work, try the reverse.