Yeah, I've used copy and paste. I though you were talking about something straight from the sys properties box.
Although I rarely ever have used it anyways, the shortcut keys that is. lol
That tutorial will show you how to upload a screenshot, preferably in jpeg format.
Basically when you're replying to a thread with the post reply button, you'd go to the little paperclip icon at the top of the reply box. The paperclip says manage attachments. you browse for it from there, in your pictures or wherever you save it and upload it. Then come back to the paperclip and it will be in the little drop down from the paperclip. Attachment 4459
The paperclip's at the quick reply box too now, I don't think it was before.