If what you're doing is trying to enter all the cities, states, lats & longs plus zip codes for a large country individually through the Etano admin panel. This really isn't the proper way to do it, adding info in the admin is more for if you just have a small country or just a few cities to add that maybe were missed or not included in the database for a country that's already installed.
You have to get your hands on a database for your country with all the info you require and have it configured for installing to the Etano database. Often the easiest way is to get a database and then convert it to a CVS file, which is basically a simple text file that can also be uploaded to MySQL.
Also, I've always felt using postal codes for a mileage or distance meter is a bad idea and not a very efficient way to do it. Especially for countries other than the US, and here's why ...
1. Many countries such as Canada, UK and Australia have a very complex postal code system. For example, in Canada there's can be thousands of postal codes for one city which is going to equate to a very large database. A database for Canada with zip codes is around 100mb, whereas a US database is less than 20mb, and I've found that UK and Australia databases are similar. In Canada and UK postal codes change every few blocks, not by district or every so many miles, which makes postal codes for these countries pretty redundant as there's no need to know the distance under a couple miles (usually 5 miles).
2. Most countries other than the US don't make zip or postal codes freely available and open to the public and therefore you have to pay for it. Sure I know if you're lucky and do enough searching you can maybe find databases on the net that have postal codes included, however having done much research into this I've found that they are often very outdated and sometimes not very accurate, which brings me to #3.
3. With countries such as Canada, UK and Australia, their postal codes are so complex and always being changed and updated, you have to use a paid service that provides updates for you, which is fairly expensive.
Since my niche and target market is the US and Canada, and because of the complexity of Canada's postal codes and mere size of the database, I decided not to use the postal codes and implement the mileage distance meter on my site, just not worth it.