Correct Interspire Cart www.domain.com vs domain.com problem

I have Interspire Shopping Cart Vendor edition, and with one of my stores, the homepage goes directly to some sort of advertisement if I type in [login to view URL], but will go to my actual website if I type http://www.websitename.com. I don't care if you come up with an .htaccess redirect fix, or solve the problem some other way, but I just want the site to work properly.