I would suggest checking out the help section, which answers this question. In short, you own the copyright on anything you submit.
One thing to remember, however, is that copyright infringement is very common online, so even though you own the work, there is little stopping others from stealing it. This is one reason that it is important to keep an eye on your posts and file DMCA complaints against anyone that steals your work.
Hubpages Help Section: http://hubpages.com/faq/#whoownscontent