As mentioned already, live view at x10 for focusing. Both BYE(BackYard EOS) and APT(AstroPhotography Tool) have good focus aids that use the live view.
Remember to limit your use of live view as much as possible as this heats the sensor considerably.
I have read that some people wind the ISO to the highest setting when using live view, this supposedly benefits the live view sensitivity, but this must be model specific as it seems to have no effect on my 60D or 1100D. I have yet to try it on the 40D.
It is possible that 'bulb' mode automatically sets the live view to maximum sensitivity.
