Either...Im guessing a screenshot would be easier.
I'm going to just post the whole process from beginning to end so if you already know this stuff, I mean no disrespect:
1. With your game window selected, hold down the Alt key while pressing the Print Screen (or Prt Scn key as the case may be) on your keyboard to get a snapshot of your game window.
2. Open MSPaint.
3. Hold down Ctrl while pressing V to paste the snapshot into MSPaint.
4. Save as a .PNG file.
5. Find an image host (like TinyPic) and follow the instructions to upload your screenshot image. It will give you an URL.
6. Copy and paste the URL (if you're using TinyPic then you want the one labeled "Direct link for layouts") into your post.
7. Highlight the URL and press the
button above the post window to add image tags around your URL.
8. You're done, so post!