One is a stripped down version of the other, and the other one is overpriced. Both are buggy, bloated, and have the despised product activation "feature". Neither will EVER be on any of my computers.
Pro has dual processor support, more advanced networking abilities, and additional security features. (Even though it's still full of security holes at the moment.) There's a list of differences on M$'s website.
I will never buy a M$ product for myself nor recommend any of their products with product activation to others. I will not buy any piece of software that Microsoft can decide to disable at their whim. The fact that the "corporate version" of XP does not have product activation present speaks volumes about how much respect Microsoft has for the home computer user.
