I want to host a service on my site that resembles MapQuest's Locator
service (http://www.mapquest.com/solutions/product.adp?page=mqlocator),
specifcally the ability to show a map based on a zip code, and
locations within 5 miles of that zip code.

This is only an example, however.

My questions are these:
*) Where can I get (for a fee, I assume) detailed and accurate maps
based on current information that I can use with my site to create an
interface for finding locations?

*) How do I resolve a street address or zipcode to a latatude and
longetude (sp?) soas to work with aforementioned maps?