I have had the opportunity to recently get my hands on an iPod Touch specifically to do web-development to work with it's fully-featured Safari web browser.
These applications need specialised formatting for these devices (both have the same resolution screens). The easiest way to identify these phones is using the User-Agent header passed in a HTTP GET/POST request.
The iPod Touch's (firmware version 1.1.1) User-Agent field (found by writing a simple PHP page to return the $_SERVER['HTTP_USER_AGENT']) is:
Mozilla/5.0 (iPod; U; CPU like Mac OS X; en)
AppleWebKit/420.1 (KHTML, like Gecko)
Version/3.0 (Mobile/3A110a Safari/419.3
The iPhone's User-Agent field (found at note19.com's blog) is:
Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en)
AppleWebKit/420+ (KHTML, like Gecko)
Version/3.0 Mobile/1C28 Safari/419.3
The above User-Agent fields have been split over multiple lines to aid legibility.