XP home as the name implies.. is meant for home use.. it has crippled stuffs here and there which the normal user wont need.
Oh yeah, nobody mentioned XP Home cannot join a domain. u need to upgrade to xp pro. but then, domains usually exists only in workplaces.
That's why if you're getting XP for a network of pcs.. better to go w Pro, u never know when you'll wanna get a domain up.
Home and Pro are equally stable. microsoft would be shooting their foot if they make they make home unstable just to promote pro. hehe.
HT simply allows a bit more speed for some heavy apps.. intel has very good "marketing" to help u understand how it works.. HT is pretty much standard now, why bother?