Erin, doing tests like this from IP can be inaccurate at times. Accuracy is around 90% at best without the use of GPS. For instance in NJ where I am located, I know certain areas that will ping outside the state to Philly or NYC.
I do have an example of what Shashank is talking about with web data lookups here: http://topliners.eloqua.com/community/do_it/blog/2012/08/06/eloqua-gated-forms-allowing-only-contacts-you-specify-to-view-your-form . If you have these users in a list already because they are existing or if you have targeted them in an email campaign introduction this may work and the data pulled via javascript in this example could theoretically be used to redirect someone to another page if they do not match the required criteria. This would require a bit of javascript programming to pull off but that article will give you a good head start.