Can .zip folders created using Windows XP Pro be opened and extracted on Mac without any additional software?
Yes.

The PKZIP format used by Windows is understood by OS X and has been this way since about 10.3. The tool used to extract the contents is called Archive Utility and it is installed by default with every OS X installation.

Your Mac-using friend can either double-click on the archive in Finder to extract it or he can right-click/control-click and select the 'Open' option from the list of actions.