Hi Anne
After you have saved the original, delete the line if you used one and go to Edit> Flatten all Objects so its now one big file.
Now go to the marquee tool and select the Square shape. Drag out the selection to halve your layout and go to Edit> Copy then immediately go to File> New and choose Okay to create a new canvas (it will automatically size its self to fit for the copied layout half) clcik on teh new canvas and select Edit > Paste
The layout half should now be on the new canvas and you can print it or save the half as jpg for out source printing.
Repeat for teh other side of the layout.
Let me know if that doesnt help - and tell me where specifically you are coming unstuck
