Have you researched AJAX at all? There are many, many simple examples out there (e.g. at
Tizag.com). What do you know about it so far?
As a general guide, you will need to:
a) create a new PHP script that receives a GET or POST parameter (presumably an ID representing a person), runs a MySQL query to retrieve a person's details corresponding to the passed ID, and returns a fragment of HTML (for example) ready to plugin to the page.
b) on your existing page create an onclick event handler and associate it with the listbox. The handler should instantiate the XMLHttpRequest object and send the request to the new PHP script, passing the appropriate parameter. It should also receive the resultset returned by the new PHP script and process it (e.g. dynamically insert the fragment of HTML into the page).
Once you understand the finer detail of how AJAX works, it might be worth using a higher-level implementation like jQuery. SitePoint have published a nice article entitled
Easy Ajax with jQuery.
Clive
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"To err is human, but to really foul things up you need a computer." (Paul Ehrlich)
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