1. Buy genuine windows 7 32 bit installation disk..
2. Go to bios set it to boot from optical drive.
3. insert to win installation disk to the optical drive and reboot.
4. follow the step by step guide to install OS.
5. At Restart Remove the disk and finis the OS installation
6. Install The driver needed.
7. The rest ...... (etc, etc,... )
As 4745454b said, it might not work properly since your rig quite old