I support a "Update my Application" feature in my SXSW 2005 schedule application. I do this by setting up a series of URLs on my webserver, one for each version of the program that was released with the web update feature:
http://2005.sxsw.com/pda/includes/downloads/update_4.1.0.htmlhttp://2005.sxsw.com/pda/includes/downloads/update_4.2.0.html
The application turns its own version string (retrieved from its 'tver' #1000 resource) into a URL using the format string
"http://2005.sxsw.com/pda/includes/downloads/update_%s.html" and then it uses that to launch the device's web browser using code derived from the Web Browser Manager sample code in the PalmSource KB.
A user with an current version of the application gets directed to a "you're using the latest version" message, while a user with an older version gets a link to the PRC download. I could also have used HTML auto-refresh to just start the download automatically, using HTML code like
<meta http-equiv="Refresh" content="5; URL=http://2005.sxsw.com/pda/includes/downloads/sxsw_2005.prc" /> embedded in the <head> part of the update page.