Just FYI, Andy's xp comparison faq needs to be qualified, you can have full ntfs file security in Windows XP Home Edition, I have XP Home and when I installed an old game (that needed to write a .dib file to the c:\windows dir every time it ran) for my daughter who has a limited account, I just booted into Safe Mode as Administrator and gave her write permission to the C:\Windows directory and then she could play the game fine.
I administer XP Pro at work (I'm I.S. Administrator) and when in Safe Mode, XP Home file permissions is identical to that of XP Pro.
Some have also said that you cannot use Remote Assistance to take over another computer with Windows XP Home, but this is not true. I use it all the time to help family/friends. What you cannot do is enable Remote Desktop and connect to the computer remotely through a Remote Desktop connection nor can you take over a Windows XP Pro computer using Remote Desktop. I have taken over an XP Pro computer using Remote Assistance and XP Home. Hope this helps.