Civicrm membership expiration date after renewal
This works in the 4.5.2 sandbox (unknown if it works in 4.4.6)


Set your membership type to rolling instead of fixed
Disable the "Grace" membership status
If you are having a membership period shorter than 3 months, also disable or shorten the "New" membership status


An alternative workaround, which however may be a bit too clunky, would be to create a new membership type monthly and update the contribution page, so that it forces people to sign up for a new membership rather than renewing their existing one. This would, however, lead to the potential for overlapping memberships if they sign up for the new membership before the end of their old one.