Now I have a question about the whole double needle thing since we are talking about it. My machine (a cheap brother xl-5340) came with a twin (i call them double) needle but no instuctions on how to use. it just says i can. Can someone explain how this would work and when you would use it (besides on this shirt). Sorry, I am still teaching myself to sew and would appreciate any help on this. Normally i would ask my mom but i don't recall ever seeing her sew with more than one needle except on her embroidery machine. and where (if you use one) does the extra spool of thread go?
A little tutorial (and I apologize for my lack of English sewing terminology!!). I've used three different kind of colour to make it easier to distinguish the different seams. I couldn't find my stretch twin needle, so you have to do with a regular one. But the principle is the same!
Here is my old old old seventies coloured sewingmachine and the twin needle:




As you can see on the last picture, the needle head is shaped like a circle but with a flat side to it. The flat side, as on every other kind of sewing machine needle, is placed away from you.
The twin needle has only one part that goes into the "needleholder" just as any other needle:

On your machine there should be an extra spool holder, but if not, you can alway use a little understitching case. Here is a picture of my machine with two spool holders:

Then you quite simply thread as you would do with only one spool. Me holding the two threads:


When you get to the needle you simply thread each pinhole:

Here is pictures of the seam:
Front of seam:

Back of seam:

When you have sewn all you want to sew, you cut off the excess fabric. If you are working with stretch fabric you will find the little snip of fabric will curl up and look even better than my hem.

I hope this is enough for you to try it out, supermedic!
~pseudo_pix