Are you able to derive or look up the math to compute the distance between two pairs of coordinates?
I believe that will require some Spherical trigonometry do compute if these are latitude and longitude figures.
Once you can do that, you can put the starting coordinates inside a pair of global fields and use your calculation in an unstored calculation field defined in your table of zip codes and coordinates to compute a distance.
You can then perform a find on this table to find all zipcodes with a distance less than or equal to a specified distance.
That list, in turn can be used to pull up all records in your accounts table where the account's zip code is a member of that list.