On the first level, before doing anything else, move to the fence on the left hand side of the level. Then keep tapping 'B' and pointing your long range attack towards the bad guys that keep coming. You'll soon get this. I got a combo of about 70, sol there's plenty of chances. This is probably the fastest 1000 points you'll ever get. I managed to get them all within 5 minutes of turning my xbox on!