Hi Paul, to expand Joudis explanation a little, assuming that you know how to enter the BIOS you should set the BIOS to boot from the cd rom as the first boot device.
Place your XP cd in the cd drive and restart your pc.
When the pc boots it will say booting from cd and then press any key to boot from pc (NB. it will reboot during the installation process and will give the same message
DO NOT touch the keyboard or else you will go around in a never ending loop, just leave it and it will boot from the files it has copied to the hard drive and continue with the installation.).
Just read what comes on the screen and select the appropriate options from the choices, the first one I think is F8 to accept the agreement (another point to note here is that you want to have a basic PS2 keyboard connected, as USB ones and other fancy multimedia or office keyboards dont always allow the F keys to work until an OS is installed and their own software added :shock: )
If you have had a big problem with a virus or damaged OS then I would recommend the option of deleting the partition that the OS is installed on when given the option, it will say WARNING as its got an OS on it etc, press enter to delete and then L (maybe its the other way round but you wil see it on the screen).
Then create a new partion in the space available and it will say what the maximum size available is, you can let it be that or decrease the size of partition if you desire.
After that it will ask you which file system you want to format it it in, depending what size of partition you made, if its 32 gig or under it will give you 4 options Fat32 quick or full and NTFS quick or full, the quick one of either will do unless you suspect that your drive is damaged, if its over 32 gig then it wont give you the Fat32 option.
After that just read the screen and type in the information that it asks for, dont forget to select UK English and GMT for the time zone, assuming that you are in the UK of course
At the end of the installation, remove the XP cd, restart the pc and enter the BIOS again and set it as Floppy and then Hard drive as the first and second boot devices.
If I have missed anything out or confused you about any part of the process please ask me to clarify anything that you dont understand