Read the instructions that came with your Lenovo disks and follow those. Only if there aren't any then do the following.

Put the Windows CD into the optical drive and shut down the computer, then restart it. It should boot from the CD.

If it doesn't you need to shut down again and restart, but this time press the "setup" key repeatedly as soon as the machine starts and before Windows does. The key varies from machine to machine and you'll have to experiment until you find it - it may be [Esc}, [F2] or almost any other key. It won't be [F1] or [F8] as they have standard meanings. Once you're in setup you need to follow the instructions carefully and change the boot order so that the CD/DVD/Optical drive precedes the hard disk.

Once you have the machine set so it will go to the optical drive before the hard disk then save your settings, make sure the Windows disk is in the drive, and restart the computer. This time it WILL start from the CD. Follow the instructions to reformat the primary partition. If there is more than one partition I recommend you to combine them into one large partition - there will be instructions to do this. Once you have one large partition, format it with the NTFS file system (will take ages). Then load Windows into your (sole) partition.

You will need device drivers for your computer to work, and once Windows installation has completed hopefully your Lenovo disks will include those. Otherwise you're getting into complicated territory and you'll probably need help.