Here is a pretty decent tute on shirring. I'm just warning you though that it does take a little practice to get it the way you want it. Every machine (and seamstress!) is different.
http://pretty-ditty.blogspot.com/200...-tutorial.html
Basically how I do it is:
1. Hand wind the bobbin with the elastic thread.
2. Start first row (make sure you backstitch!)
3. do as many rows as you need using the presser foot as your guide. (at least 3 rows for optimal stretch.
4. finish off by backstitching and tying the elastic thread off
5. with garmet wrong side out, Steam the heck out of your stitches you just made.
I will say that shirring is a tad more difficult with a drop in bobbin. Good Luck!