I've just started looking into Silverstripe having developed a couple of sites in Wordpress and found it not quite fitting my needs. Open Source is great but a client will always ask for bits adding on.
So... I am looking a add a zip code locator such as 'Lookup Runner' to my silverstipe site http://www.lookuprunner.com does anyone know if this sort of thing is possible.
Yes, you can add PHP code from other sources into your SilverStripe site. A common practice is to create a "thirdparty" directory in your mysite folder (or module folder, if you're creating a module).
You may want to exclude that PHP code from being included by the manifest builder when a dev/build is run. This can be achieved by creating a file called _manifest_exclude in the folder that contains the third party code. (Note the leading underscore).
Then you can require() that code as requires in your site logic.