In order to take a screenshot you must:
1) Root your Atrix
2) If you don't want to root your Atrix, or just would like an alternate method, read this great article as a workaround.
3) Programs used to capture screenshot (Root Required): ShootMe, drocap2
4) Please host pictures on a site such as Photobucket or Picasa, and then use the insert image tool above to add them to your post
If you use any cool and/or interesting theme's, homescreen replacements, or widgets, please list them in your post also.