You can deny by referer (sic) but it isn't what you want here. The referer isn't the visitor itself, it's who sent them to you. That is: if you click on a link to go somewhere, the "referer" is the page where you clicked the link. You probably want the user agent.
:: shuffling papers ::
Can't imagine what's taking g### so long, but earlier today at the end of a thread* I posted an idiot-level explanation [webmasterworld.com] (sorry) of what you can expect to see in your raw logs. Almost all of that information is also available to your htaccess; you just need to find the part that is unique to the site. As wilderness said, probably a combination. Say, IP address within a certain range, and user-agent that includes certain attributes.
* Someone explained to me how to link to a specific post, but now I can't find the explanation. The long post timestamped 1:18.