Forum Moderators: rogerd
Once you have a focus, promote the forum elsewhere on the site. If you are using it for customer support, then mention the forum prominently on the FAQ page, Contact page, and other places where customers might look for support.
If you want to talk about your products, link to the forum from the product page, preferably to a specific forum or thread.
Assuming that the ecom side of the site gets a lot of traffic, then you'll definitely start getting more pageviews in the forum.
At the same time, you'll need to ignite some discussions and fan their flames - the Community Building Library [webmasterworld.com] has some good discussion of how to jump start a forum, how to turn lurkers in to posters, etc.