WordPress Redirect based on IP address

I have a bunch of wordpress blogs, and really all I need is a tool (probably implemented through .htaccess) that compares the IP address of each visitor to my wordpress site to a known list of IP addresses.? If the visitor's IP is on the list, nothing out of the ordinary is to happen.? If the visitor's IP is not on the list, then redirect that visitor to a URL I'll provide to you. The list of IP's will be provided in the form a text file. This is really a very simple project if you know anything about wordpress and .htaccess.? I'd prefer if this was implemented as a wordpress plugin, but my preference is to have this solution sooner rather than later, so if it's easier to do it in some way other than as a plugin, that's fine.