I'm also going to photograph the all souls procession...
I don't think image stabilization is going to be of too much help here because at the light levels we're talking about, it's not shaking or vibration that's going to cause blurriness, it's going to be the moving subjects. Even at wide open f/1.8 ISO 3200, I think we're still going to be looking at shutter speeds that are slow enough to cause significant blurring of the people walking by.
The two lenses I'm going to take with my canon XT are the 50mm f/1.8 and 28-135mm f/3.5-5.6 IS. I think my best friend at the parade will be my Manfrotto 190 tripod. I'll probably walk around with it in monopod mode. I'm also going to take my speedlite 430 and use it in curtain flash mode to try to have a good blast of flash to "freeze" the subject and reduce the visual effects of the movement blurring, but this won't increase the shutter speed at all.
In all, it's going to be very challenging, but it will be interesting to see what we come up with.