A good place to start is here if it has a physical location: http://www.google.com/mapmaker

From mapmaker you can close the business (it isn't immediate as they use crowd sourcing).  You can also report the business as being closed through the maps listing.

If you do a search for the listing in question, in the list view (http://maps.google.com) you'll see an option that says 'more' with an arrow pointing down.  Click that and hit 'report a problem'.

Hope it helps.

It certainly could. Google sees the www. version as a 2nd website, so essentially you're splitting your 'ranking authority' between 2 webpages.