This is a really cool tip and shows you how to combine layers without flattening the original layers
You have an image composed of several layers and you want to create a new layer that has the entire image merged, while still maintaining all the seperate layers .
Create a new layer and make it active.
Link all the layers together, by clicking to the left of the thumbnails,
you will see the little chain, indicating that the layers are linked.
(IN Photoshop CS2 Click the top Layer. hold shift and click the bottom to select all layers)
Now while holding down the Alt/Option key, click Merge Linked
from the layers "fly-out" menu.
(Also work from merge Visiable)
And ZAP! You now have a new layer with the info from all the layers combined into it without merging the the layers. I don't know about you, but I think that is pretty slick!
In Photoshop CS 2 all you need to do is click on the top layer and press Ctrl+Shift+Alt+E (Cmd+Shift+Option+E on Mac) CS2 will create the new layer on top or you. On CS do the same thing but make a blank layer first.