If you installed Mountain Lion, it should have created a Recovery HD or warned that it couldn't and stopped the installation.
If you have a wireless keyboard, you may have to time the button press right after you hear the startup tone.
You should also be able to see it if you start into the boot manager by holding down the option key. That should present all the bootable volumes.
If you don't mind give this a try:
Boot Using OPTION key:
1. Restart the computer.
2. Immediately after the chime press and hold down the
3. Release the key when the boot manager appears.
4. Select the desired disk icon from which you want to boot.
5. Click on the arrow button below the icon.
In the above at Step 4 you would be looking for a listed disk called Recovery HD. Do you see that listed as an option?
If you have mountain lion or lion installed you can use the Recovery HD. Those articles were discussing Internet Recovery, which boots from Apple's servers.
The Recovery HD is a separate partition on the hard drive which allows you to boot from there to repair or reinstall.
Please let us know if you can get into the Recovery HD as I noted above.
No what you looked at was for Internet recovery. Newer Mac's can boot off of and install from Apple Servers if the disk doesn't have the recovery partition.
However all ML systems wil have the recovery partition if they were installed correctly. The only way you'd be missing it is if you had to replace the disk in the system, Then you would need to go back to the original boot DVD's and start from there.