> Unfortunately I didn’t get very far with my initial testing
> this afternoon because I’m in an environment where I have
> to use an HTTP proxy server to access the net, and
> ClamXav appears not to support proxies at first glance.

Actually, there is a small helper process called "ClamXavProxyHelper" which runs during setup and attempts to accomplish what you explained here. Unfortunately it doesn't work for everybody and apparently you are one of those. Some have been able to fix things by simply launch it via the Terminal app, but even that has not worked for all.