First open up the image with the piece of Lace you want to use. Point at the layer with lace itself (most the time to have a background layer too, so don't mix that up), copy and paste as new layer. Close the original.
Create a new image 500 x 500 px with a transparent background. Floodfill the layer with any color of your choice (doesn't make any difference which one, we change that later anyway). Insert your lace (it's still on the clipboard) with "paste as new layer". You have 2 layers now, one with the background, one with the lace.
Now add a guide line somewhere close to the left border (you can't see that on the picture above, but it's supposed to be where the red arrow pionts). We need that so our lace pieces will be correct in a row. Don't forget to enable "Snap to Guides" in your Menue "View".
Now move the lace close to the guide and you will see, that it will "snap" right on to it as soon as you're close enough.
Go to your layers palette, activate the layer with the lace and duplicate this layer one time. Activate the duplicated layer. With your move tool arrange the second lace above the first one. Use the arrow keys to get it as close as possible to the first one. If you do it correct, you shouldn't see any space between the two pieces - but the design shouldn't overlap either! Repeat this step one or two times until your lace border is close to the bottom and upper border of your image.
Now go to your layers palette, close the background layer (the one with the color) by clicking on the eye, pick anyone of the lace layers and go "Merge - Merge visible". Leave the bottom layer still invisible.
Make your merged layer active. With your Magic Wand Tool click one time beside (not ON!) the lace in the image. Go to "Selections - Invert". Next go to "Image - Crop to Selection"
and now you have something like this:
Open your background layer again. It's time now to delete the color on our background layer: Make the background layer active by clicking on it in your layers palette and hit the Remove Key on your keyboard (don't delete the layer!). Your background layer should be complete blank/transparent now.
We have to adjust the size of the image again, so you can continue making your stationery. Therefore go to "Image - Canvas Size" and give the image some new dimensions.
What's interesting now is the HIGHT of your image - you have to transfer this from "Original Dimensions" into the section "New Dimensions", like I did it on the picture above. Make also sure, the "Placement" has the arrow in the left upper corner activated. The width is up to your choice, whatever you want your stationery to be; I decided to take a width of 1024 px.
You're done! Now you can continue to complete your stationery.
Since I make stationeries for Incredimail, this lace border stationery would look like this afterwards:
