Just installed another instance of Apache? Not appearing in the Apache Service Monitor? Read on...
I installed Apache 2.2 on my local machine as I hadn't used my current install of Apache 2.0 for a while and the httpd.conf file was looking a little bit messy.
I didn't install it as a service for reasons that escape me and I soon grew tired of having the command window open whilst it was running.
A little digging revealed that you can add it as a service by running the following in your new installs bin directory:
httpd -k install
This seemed to do the trick for me and now I have Apache2 and Apache2.2 as options in the system tray Service Monitor.