Before you re install Windows remember to download the Network driver and save it to memory stick or CD. This is so that you can still access the internet to download all the other drivers your PC will need.
Put the install CD into the drive and reboot your pc.
When the PC is booting you will see black screen white text which says " Press any key now to boot from CD"
Literally press anything.
This will load to a blue screen and it will begin to load everything.
When its finished loading you will need to delete the old partition (assuming you want a totally fresh install)NOTE YOU WILL LOSE ALL DATA
The on screen instuctons will tell you how to delete it. Once thats done, select the unpartitioned space and click C, this will create a new partition, once you press C it will take you to another screen, here it has used the free space you have on the hard drive and has set it to the size of the partition.
Carry on creating the partition, again the onscreen instructions are straight forward.
Once thats done it'll take you back to the screen you was at previously and all you now need do is (i think its return) hit return and install windows.
Wait for the process to finish, the computer will reboot and then you can do the easiest part of the set up.
Setting your location, the time, what timezone your in.
You should be fine!
Also if anyone else can explain this better than me please feel free to pick up on anything you think I've missed. Even though Im pretty sure that just about covers all he needs to know ?
Anyway Hope this helps and thanks