Follow neallewis and up the iso setting the 1100 is good for that, I have just been following a thread somewhere else and this page was recomended, and no I don't understand it more than to say you possibly won't notice the change in the picture at 800 and can push to 1600 before you may, this will allow faster shutter speeds, (every thing is a factor of 2).
http://www.fredmi.fr/en/rebel-xs/2-l...eos-1000d.html
If you are shooting at 1000/sec and can keep the lens aperture in the middle (say F8), to give you some depth of field, then that's the best you can do, try different settings in the street, passing cars etc, see how they compare.