That got it working. But any idea why I'm only getting about 5000khps? Seems like something's wrong...
Did you try using -f 1? That improved my performance on a 5970 from about 15M Hash/s to about 330M Hash/s.
I have no idea why DiabloMiner is affected by the -f option so much more than poclbm, but apparently it is.
Also, is there a way that we can have DiabloMiner output all those interesting statistics about mining like the modified version of poclbm that's been going around here? (Invalid/Stale Percentage, Current position in the getwork, Ratio of getworks to submissions, hashrate, ratio of getworks to answers with more work in them) Those were great for getting a very condensed picture of how your mining is going.