geographical queries?

we import a database that has among other things, listings of locations by address, city, county and zip, and our customers would like their website to have a 'within $x miles of $address $city $zip' search in addition to the other searching they already have. another customer would like to have a click on the map to do a search of within 25 miles of where on the map they clicked on the same database. anyone have any pointers, tips or links on how to do either of these searches? the database changes frequently (nearly daily updates from a 3rd party that currently is having problems filling in all the fields they said they would give us) and contains over 10000 records, so it wouldn't be practical to add information to the records manually to facilitate a location/distance based search. we do add some additional fields automaticly, so it won't be a huge problem/rewrite to add additional columns in an automated fashion.