Indeed. And, just to be completely clear:
1) Decide which version of Windows you want to use going forward, and insert the appropriate CD in the drive.
2) Restart the machine - it will start to boot from the CD and begin the installation process.
3) Very soon after, it will find the existing installations and ask how you want to proceed. At this point, do not choose any of the options which look like upgrade or dual boot or anything like that. Choose the option that says you want a new installation of Windows.
4) Then, it will ask you where you want to install it. This is the key thing. You will see existing partitions on your hard drive (sounds like there'll only be one anyway) - make sure you delete them all so that there is nothing left but unpartitioned space. Choose to install Windows on the unpartitioned space, and it will create a new single partition, format it (choose NTFS), and proceed with the installation.