Assumptions:

Red Hat Linux 6.2 Install server with
Apache 1.3.12-2
PHP Version 4.0.3pl1

See other Documents for installation of PHP

1. Log in as root

2. Download the file
nmap-2.53-1.i386.rpm
to your Web Server

3. Install it by typing
rpm -iv nmap-2.53-1.i386.rpm

4. Check out the following PHP samples for setting up web pages
scanform.html - This form takes an IP address for scanning
result.php - This form display the scans for ports 1-1023.