20 x 30 poster question

[Crypto]

No problem. Like you, I also shoot hi-res images and had to add 2GB's of RAM to help me out.
The "Empty Clipboard" option is under "EDIT". Not sure if it's in every version, but it should be. I have XI

Are you using layers to add each photo, or just adding every photo to the same background? When I do this, I create a new layer for every image.