Depends on what program you are using on the PB. Mail? Thunderbird? Entourage? Where are the contacts? In the email program address book, or in OSX's Address Book?
If they're in OSX's Address Book, just open it up, select the contact (or the group), Control-Click (or right click) and select "Export Vcard". Save that file and import it into the contacts list/address book of whatever email program/address book you're using on the PC.