Today I tried to boot one old Compaq PC without Keyboard, but failed. Later had few searches and finally found a link from Paul Battley's website. Here is the link. This worked Fine.
It is not at all complicated.
1. Go to Bios setup
2. Set a power on password (it will ask for retype the password). Don't worry it will not ask at the time of boot
3. Just below the Power on Password option (main menu) there is one Password options, click on that
4. Enable Network server mode
Now save and reboot.Now your machine will boot without keyboard.