First thing is to back up all your docs, pictures, IE fav's and emails. Burn them to a DVD or cdr disk. Or transfer them to a usb stick or an external hard drive, if you have one.
Do you have a full windows disk ( oem or retail ) or a manufacturers restore disk. If you have a restore disk, what is the make and model of the computer.
" Ay programs which I have used a serial key for on my PC, will they be able to work on my PC after reformatting? meaning will I be able to reinstall them without the software saying thats its already been registered?"
If you have the installation disks and the serial keys, they will be fine.
" Lastly, will XP be easy enough to load back ontop the PC? "
If you have a full retail edition, an oem disk or a restore disk. Windows will format the drive and load XP for you. You will need the drivers for peripherals, keep them handy. the main thing is to be able to get back onto the internet. So have the modem driver disk handy, if you have one. if you connect via a router, you shouldn't need one. also you ISP disk.
If you can do all that then>>>>>