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The 1-series is Canon's flagship line. It has been that way since the film days. The 1Ds probably just has the "s" to differentiate it from the 1D. The 5D is only available in full-frame, so the "s" isn't necessary.
From what I know, the 1Ds Mark III came somewhere in Q4 2007.
A few months...
A flash is effectively instantaneous. The amount of flash light picked up by the sensor is the exact same no matter your shutter speed. The shutter speed will only change the amount of ambient light. If you want to change the apparent effect of the flash you need to adjust aperture.
A lot of...
I've cleaned my sensors using specially size swabs (with a flat edge the exact height of the sensor) with a few drops of liquid.
See the left half of this pic:
Once the camera is in cleaning mode and the lens removed, you open the packaging for the swap, put a few drops of cleaning...
The red lines are the focus assist beam. They help your camera focus.
As far as the flash "not working" indoors: Is it firing? What mode are you in, manual, multi or E-TTL? What sort of exposure is the camera set to do? What camera body are you using?
The pop-up flashes on Canon's dSLRs...