Can I replace windows 7 to XP and what would I not be able to do if I did
Yes.. You can upgrade Windows Vista And 7 to XP Pro. Many of the Factory assembled machine have the boot drive in AHCI mode... To keep this you need to down load and install the AHCI driver at the beginning of the install process. You will need a floppy Drive as MS, always being behind the technology curve, failed to allow XP to install a driver from any other drive letter than A:.
Or you can set the drive to normal IDE mode in your BIOS/CMOS.
Yes, if you have a Windows XP installation CD and an installation key. You would need to boot from the CD, format the hard drive and install Windows XP. After that you need to install needed device drivers (video, audio, etc) from the website of either your PC manufacturer or motherboard manufacturer if it's a hand-build system. Any information on the hard drive should be backed up beforehand since it will be deleted during the format process.
I think he is asking if he can go from Win 7 to XP not XP to Win 7. I do not believe that there is an official downgrade path (there was with Vista in some circumstances). However you can install XP if you wanted too assuming you have the right licence for it. You will however lose support for larger memory configurations. XP does not handle multi core CPU's as well. It is losing support from third party software providers and it is not as stable over time. It cannot handle having as many applications installed on it. I could go on but essentially XP is a ten year old operating system. In some cases it uses less resource but so does DOS.
Why would you downgrade to xp, (XP doesnt have support anymore),W7 is so much better in my opinion, at this point Microsoft already said that they wanted to 'eliminate' XP from market.
Anyway, you could install a XP on your pc,but you will probably have to spend more time with the drivers because if your pc has W7 on it it probably has newer hardware,then you will need to find xp drivers. Also it depends on what you use your PC for, W7 uses DirectX 11 which is a big improvement in graphics and multimedia.XP uses DirectX 9. Windows 7 security is much better than XP.
To be honest, just keep W7 it is safer and has better performance,better memory management,better power management. You will be probably more limited to use latest software updates for some applications and more.I hope it helps