I have an SD7, which is very similar to your SD5 and
AFAIK, the only way that you are going to be able to do what you want to do: namely to dump the stuff from the camcorder to the external drive via USB is to buy a "Personal Storage Unit" which acts as the USB host. I don't think that the USB host mode of the SD5 is designed to do what you want.
You need something like this:
http://www.amazon.co.uk/NextoDI-Next.../dp/B000KEBASM
which I am assured takes either USB or you can just bung in the SDHC card. I was told that the 2325 will take an 8GB SDHC so I bought one (2325 that is) but in the end I never used it, preferring to buy extra SDHC cards instead and take those on holiday because they only weigh 2 grammes.
I bought too many, of course.