A quick answer No. If you transfer camcorder material via USB you will not be able to download sound. Or at least I can't on mine and of course as you say it is quicker. Hope this helps. Regards Carper
The danger in using USB to transfer camcorder material is that the speed of transfer is not as fast as Firewire and that, therefore, frames may be lost from your data. This could result in a "jerky" playback. Remember that you are normally transferring about 26 frames per second - USB can't really handle that.
If you haven't got a firewire port on your laptop, you can get a firewire adaptor card. It is not an expensive item and should solve your problem. All computer stores should have them in stock or you could google "firewire adaptor card".