To clarify what Mark has said:
For a camcorder to be able to do analogue passthrough to a PC via firewire it
must have DV-in & AV-in. Some cams will have DV-in only and many others will have neither*and therefore can
not do analogue passthrough. Only the higher models in a range tend to have AV-in on them, although all Canon models where the model number ends with an 'i' have the inputs.
* due to EU tax laws a camcorder with inputs is classed as a VCR and this makes the tax payable on it higher and therefore the price we pay higher
Mark.