Hi Glenn,
If you haven't found a good program yet for stitching plans together, try Inkscape. (
http://inkscape.org/)
It is basically a drawing program but seems easy to use.
My plan sections are in JPG format and I could open them in Inkscape.
Basic procedure was to do this:
1) Start Inkscape
2) Create a new drawing
3) Edit the sheet size to be big as you need. (File Menu / Document Properties)
3) Open JPG file in Inkscape.
4) Select All then Copy.
5) Switch to big sheet then Paste.
6) Move the pasted image around until you like where it is.
7) Use the Transform function to Rotate the image if needed. (Object menu)
8) If not done go back to step 3.
9) Save (Or Export if you want bitmap)
You probably want to use a different program to clean up the bitmap (dust spots etc).
Good Luck!
Chris