If you have a Lexmark x7170 (or any 7100 Series Printer), then you should be able to do double side printing. This is a little bit tricky but not very difficult to achieve.
Benefits of duplex printing and method below:
1) Saves paper and saves trees and helps the environment.
2) Printing is faster if you intend to print double sided and were planning to do manual feed of 2nd side of paper.
Let us assume we have a print job of 9 pages.
So once you hit the "Print" command of your application, the Print menu should pop up. Then click the "Properties" button. This should open the "Lexmark 7100 Series" dialog window. On the left hand side, there is the "Print Layout" section. There click the "Two Sided" link. Now you get a change in the window content and you should see "Duplexing" on the right hand side. Now check the "Two Sided" check box. Uncheck the "Print Instruction Set" check box (remember, we don't want to waste paper). Click ok. (NOTE: You should have the "Print Last Page" checkbox checked).
You should have loaded up a bunch of paper into the tray for the printer to print. The printer will function smartly and print page 9, 7, 5, 3 and 1 on the papers. Then it will pop a window asking you to take the stack of printed pages and feed it back to the tray by rotating the orientation (do not reshuffle or change the pages). Once you have fed the paper to the tray, click the "Continue" button. Now the printer will gleefully print pages 2, 4, 6 and 8. Then it will just chuck the paper with page 9 on it. We are done.
* If your current set of paper is precious like you are printing on expensive paper or letterheads etc, do not attempt automatic duplex as the printer spool may feed in 2 papers at one shot and mess up the printing order.
* Print one set at a time. More than one set can cause problems.