The facts:
XP Home is in the "Consumer, Hardware, Multimedia, and Microsoft Dynamics" product category according to the
Microsoft Support Lifecycle Policy FAQhttp://support.microsoft.com/gp/lifepolicy. As such, it receives mainstream support for 5 years after release or 2 years after the successor product release
whichever is longer. Assuming Vista is released sometime in 2007, then XP Home will continue to have mainstream support until sometime in 2009.
XP Pro is in the "Business and Developer" product category. As such, it receives mainstream support for 5 years after release or 2 years after the successor product is released, whichever is longer. In addition to that, it then receives extended support for another 5 years following the mainstream support phase, or 2 years after the second successor product is released, whichever is longer. Thus, with a Vista release in 2007, XP Pro will go from mainstream support to extended support in 2009, with extended support until at least 2014, possibly longer if Vista's successor isn't released until after 2012.
Both mainstream and extended support phases include security updates. However, the security updates will only be available via manual download (not on the Windows update site) after the extended support phase is in effect for 2 years. (Thus, in the above example, XP Pro will have security updates on the Windows Update site until 2011, security updates available only via manual download after that). XP Home won't have an extended support phase, so security updates for XP Home would theoretically end sometime in 2009 if Vista was released in 2007.
Now that we have that cleared up, full list of differences between Home & Pro:
1. Pro includes Remote Desktop (login and take control of the desktop over the network from a remote location), Home does not. This is not to be confused with Remote Assistance, where someone else can control your desktop with your permission (both Home and Pro have this).
2. Home supports ONE physical processor (regardless of the number of cores or hyperthreads). Pro supports TWO physical processors (regardless of number of cores or hyperthreads). This means that if you have a dual-core hyperthreaded processor, XP Home will support it and show four virtual cores in Task Manager.
3. Pro has the replacement for the Windows Backup program installed by default, for Home it must be manually installed from the CD. The Pro version contains Automated System Recovery (ASR), where the backup can be used to resurrect a system that won't even boot or has to have the hard drive replaced. The Home backup program does NOT support ASR, even though there are still references to the technology in Home's version of the backup program.
4. Pro supports dynamic discs which can do software RAID 0 and RAID 1. Home does not.
5. Pro has the Windows Fax software installed automatically, for Home you must install it manually from the CD.
6. Pro has Internet Information Services 5.1/Personal Web Server, Home does not.
7. Pro supports the Encrypting Fle System, where files within certain local (not network) folders can automatically encrypt all files within. Home does not.
8. Pro supports file and folder-level security access control, home does not. (Home does support share-level access control for peer-to-peer networking).
9. Pro can be a member of a windows domain, and can be centrally managed via Active Directory. Home cannot.
10. Pro can be managed via group policy, both via the network and locally using gpedit.msc. Home does not have group policy security control.
11. Pro supports IntelliMirror software deployment and Remote Installation Services, Home does not.
12. Pro supports roaming profiles where a user can get their personal desktop settings by logging onto any machine in the domain. Home does not.
13. Pro supports multiple languages in a single install. Home can only be installed with single language support.
14. Pro supports the SysPrep tool (used to prepare machines for upgrades from an older OS to XP). Home does not.
15. Pro supports the following extra networking services: IPSec, SNMP, Simple TCP/IP services, SAP Agent, Netware client, Network monitor. Home doesn't support these.
16. There are a few differences in the default user interface: In Pro, Guest logon is disabled by default, in Home it is turned on. In Windows Explorer windows, Pro shows the address bar by default, in Home it is hidden. In Pro, there is an option to show Administrative Tools in the start menu, this is missing in Home.
17. When using peer-to-peer networking, Pro supports up to 10 connected machines. Home supports up to 5.
18. Pro supports Offline Files, Home does not.
19. Pro supports the Scheduled Tasks console, Home does not.
Under the hood, Home and Pro share the same kernel and the same inner workings. Security between the two is virtually identical if the same patches are applied.