I have had experience with a friend who had the same problem you are not perhaps running a brand name computer are you? and if so, they all have a backup partition that looks on windows like another hard drive or perhaps running a dell? anyways there is no other possible way that i have ever seen that xp pro runs slower than xp home not even on it's worst day of course that is just me. BUT most likely you need to run a program called powerquest partition magic or another program before installing win xp and just completely delete the backup partition or if you could run a format on that partition which i don't think actually will work but yo want the hd you are running on to appear as one hard drive to windows and not two unless of course you are running two or more hard drives. What seems to happen is the manufacturers backup partition seems to try to install itself onto win xp pro and it just doesn't work and also you get all of the bs programs that you don't want starting on installing themselves from that backup partition I don't understand how it works but what i can tell you is you need to make it go away.
I just recently upgraded from XP Home Edition to XP Pro, and have noticed that my computer has been moving quite a bit slower than it was. Applications seem to be taking up more of the cpu than they used to, which is probably what is causing the drop in speed. There are no programs running now that were not running before the upgrade (including services). I am using Norton Antivirus 2004, so I don't believe that it is a virus. If anyone has any ideas about what would be causing this, or how to fix it, it would be a huge help. Thank you very much.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic