I am not 100% sure, but I think the XP version of MS Hearts is an "updated" version and does not allow you to play multi-player. I only say this because it seems that a lot of "Internet" games come standard on an XP install these days. Internet Hearts, Internet Spades, Internet Checkers... etc. I would go with playing the 98 version
I wonder if you can copy the hearts file from a 98 machine over to an XP machine and have it work like we are all use to.. with multiplayer support