Store locator / postcode proximity

Hi folks, I've seen messages on here in the past about "Store Locator" tools, where someone enters a postcode and the nearest store to that postcode is found. I'm wondering if anyone has any information about how to get the proximity data for postcodes in Australia? Or is it safe to assume that if a postcode is, say, 3107, that 3120 or 3110 (for example) are nearby as well as 3108 (so, perhaps, 10 above and 10 below could be safely assumed to be "nearby"?) I saw some mention of this a few months ago here from some of the other Aussies on the list, but I've long since lost the archived messages. Could someone please help me a little with this? :) Thanks Jason -- Jason Murray jasonm@melbourneit.com.au Web Developer, Melbourne IT "Work now, freak later!"