vb.org Archive - Sorting by distance

I've installed a zip code database and want to implement a search feature that will show posts in a forum within x miles (I've also added a custom thread fields hack to collect zip codes in that forum). All posts in that forum will have a zip code field. I'd like to make it work similar to this but can't figure out exactly how it was done:
http://www.jeepforum.com/forum/forum...zip2=50&model=

Does this look like a plugin for forumdisplay that adds the distance sorting code? Any ideas on how it might be structured?

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(1)ad_footer_end
(1)ad_footer_start
(1)ad_header_end
(1)ad_header_logo
(1)ad_navbar_below
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Phrase Groups Available:

global
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Included Files:

./printthread.php
./global.php
./includes/init.php
./includes/class_core.php
./includes/config.php
./includes/functions.php
./includes/class_hook.php
./includes/modsystem_functions.php
./includes/class_bbcode_alt.php
./includes/class_bbcode.php
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Hooks Called:

init_startup
init_startup_session_setup_start
init_startup_session_setup_complete
cache_permissions
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X vBulletin 3.8.12 by vBS Debug Information
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Template Usage: (1)ad_footer_end (1)ad_footer_start (1)ad_header_end (1)ad_header_logo (1)ad_navbar_below (1)footer (1)gobutton (1)header (1)headinclude (6)option (1)post_thanks_navbar_search (1)printthread (1)printthreadbit (1)spacer_close (1)spacer_open Phrase Groups Available: global postbit showthread	Included Files: ./printthread.php ./global.php ./includes/init.php ./includes/class_core.php ./includes/config.php ./includes/functions.php ./includes/class_hook.php ./includes/modsystem_functions.php ./includes/class_bbcode_alt.php ./includes/class_bbcode.php ./includes/functions_bigthree.php Hooks Called: init_startup init_startup_session_setup_start init_startup_session_setup_complete cache_permissions fetch_threadinfo_query fetch_threadinfo fetch_foruminfo style_fetch cache_templates global_start parse_templates global_setup_complete printthread_start bbcode_fetch_tags bbcode_create bbcode_parse_start bbcode_parse_complete_precache bbcode_parse_complete printthread_post printthread_complete
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