Wel you can screen capture on ipod/ipad/iphone by pressing home and lock at the same time. Then either upload the picture using an app like photo bucket to the internet or email it to your self.
Photobucket: The pictures you uploaded will appear in an album under the picture you will find and image tagg. copy this tag and post this in any post and the picture will apear.
Image Code:
If you used email you will find your picture in the mail and you can upload the picture to imageshack/tinypic or some other site or photobucket ofcourse and post the tag in your post. or you can use Uploud Attachment which will appear each time you want to post something. You can Choose File and add a comment. this will look something like this: