I'm sorry, I'm newbie...

I have installed GametrackerLite. I have Half-life and Natural Selection. They're all installed. In servers page, I click on "join" but it sends an error:

"Unable to launch requested game as it was not detected as installed. Please setup the requested game and try launching again."

Actually, I'm not sure it's installed... I know that we must see in Half-life/Custom Game menu. But there are only Team Fortress and Deatmatch.

What should I do? Please help me.

Thanks.