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.

And you can go the other way as well. Select an item or folder and hit Compress under File in Finder. It will make a compatible .zip file you can send to a Windows user.

Yes, OS X can natively extract .zip files. You should be fine sending it.