I downloaded HALO Custom Edition, ran it with the -screenshot in the command line.  Found out that CE servers must be separate from vanilla servers.  Or did I screw something up?  I only got about 6 servers to show up with CE.
I put the -screenshot in the vanilla command line and I didn't get screenshots either.  I know it's possible because I've seen screenies.
Ideas?

the print screen button.

Then exit the game, and open a image program (I use Photoshop CS2), open a new file (at the resolution the game was running in, when opening a new file in photoshop while you have an image in the queue, it will automatically make the parameters of the file at the resolution), and then paste.

That is how I do it.  I know there are utilities out there that will get screenshots also (FRAPS comes to mind).

Hope that helps.

Ah ha!  So print screen will throw it on the clipboard.  Not what I had in mind but better than nothing.  Thanks!  I'll try it.

I thought there was a key in the game, like F12 or something. if so going into the options for the controls will show it
but maybe I used the print screen method when I did it in regular Halo
I know I didn't mess with any command line arguments

Finally got it to work last night.  I'll just have to open up Paint, then start playing and paste the pics to Paint and save real fast between games or when I die in-game.