Mike,
You can try the following for scanning double sided documents, assuming you have a document feeder.
1. Load the pages on the scanner - the front of the first page should be the first page scanned.
2. In the xsane app:
a. Select the option for ADF
b. Select a directory for the scanned pages
c. Use any file name you want, but put -001 at the end (before the .pdf)
d. Set the page count to +2
e. Click on scan
3. Once the scan is done, take the pages from the scanner and put them upside down in the document feeder. The bottom of the last page should be the first page scanned.
4. In the xsane app:
a. Set the page count to -2
b. Click on scan
When done, you will have scanned documents with <filename>-0001.pdf, <filenme>-0002.pdf, etc. in the directory you selected in step 2b. The odd pages (ie -0001, -0003, -0005, etc) are the front facing pages, and the even pages are the back of these pages. You can use any number of tools to combine these into one pdf document. I use pdf-shuffler. You can add all the scanned documents into pdf-shufler, and print one large pdf with the fronts and backs in the right place.
Hope that helps!
Mark