to a 64 bit Operating System such as memory use, support of hardware DEP rather than thorough software, kernel patch protection, mandatory driver signing, enhanced security features, can access greater amounts of RAM (64 bit Home basic 8GB, 64 bit Home Premium 16 GB, 64 bit Business, Enterprise and Ultimate 128GB while ALL 32 bit versions max out at under 4 GB).
Disadvantages are that 32 bit apps are not any faster even with the added memory, some 32 bit apps are not fully compatible and must be run in XP Mode, doesn't handle 16 bit apps at all (DOS subsystem is no longer present at all), no support for 32 bit drivers, mandatory driver signing, manufacturer's often opt to not update drivers so you have to get compatible peripherals.
XP 64 bit is not "based on the Windows server 2003 kernel" any more than XP 32 bit is "based on" the 32 bit Windows server 2003. 64 bit versions of XP and Windows server were simply first generation and didn't sell to very many individuals or businesses for several reasons chief of which is that hardly any manufacturer's wrote any 64 bit drivers for their peripherals except for the really high end peripherals and software publishers weren't offering much in the way of apps optimized for a 64 bit OS so a fair amount of the actual 64 bit software that is out there doesn't run very well if at all on the older 64 bit XP.
To summarize all that, if you are staying with Windows XP stay with the 32 bit version to avoid MANY, MANY problems. If you opt to upgrade to Windows 7 go with the 64 bit and more RAM UNLESS YOU HAVE LEGACY 16 BIT APPLICATIONS that you need to run.
PS - you might note that mandatory driver signing is noted as both a pro and a con because sometimes it is a pain in the gluteous maximus.
So here is my question, is there any notable advantages of using a 64-bit OS over a 32-bit OS. I wish to know because I love Windows XP however the only 64-bit version I have ever found of it is based on the Windows 2003 Server Kernel therefore not really being XP right? Anyway I have a 2.20GHz x64 processor does it make any major difference to use a 64-bit OS? Thank you in advance for your answers!