When I last upgraded my machine I asked the same question. Apparently there is some advanced networking stuff in XP Pro which is useful for large networks but is unnecessary for the home user, hence XP Home is available without this and is therefore cheaper. I was advised that XP Pro is much better developed and you are less likely to run into trouble with it than if Home is used. Since I got it, I have had absoloutely no trouble at all even to the extent of setting up a radio LAN with our 2 other Win 98 machines which was easy peesy (it virtually did it itself). I have also heard of one or two people getting XP Home and then being obliged to buy the upgrade because they have run into problems. It may not be so bad now that XP home has been out there some time and maybe Mr. Gates has produced some fixes for its alleged problems.
P.P.