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The main difference I have found for photography of comets through a telescope (quite different to wide field fixed tripod stuff like McNaught last year), is processing. You need to align the images on the comet not on the stars. Not all software will do that. I do it using CCDSoft and it's centroid alignment capabilities.
Other than that, I agree with keeping the exposures short, for simplicity. The exposure time depends on the rate of movement of the comet, but I often find 30-60 seconds isn't a problem. Also if you're just wanting a pretty picture you can push the exposure time a little longer than if you need a dead steady comet for analysis, as a slight bit of trailing in the comet head isn't usually noticable.
There is software out there which will tell your telescope to track at the correct rate for the comet. I asked in this forum about it a while back (maybe 6 months or so) and got some replies but have forgotten it's name - I'd suggest searching here. I haven't tried it, but even if it's half good, it'd mean an increase in exposure time before trailing of the comet head which would be beneficial.
As Ian said, equatorial is much better. I'm not sure how you'll go Alt-Az. Alt-Az short exposures of general starfields is OK because you can use programs like RegiStar to align the images can cater for field rotation in doing so. But for a comet, where you're aligning on just the head of the comet, I'm not sure how you'd cater for field rotation unless the comet is moving slow enough that you can do a normal alignment on the whole starfield.
Roger.
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