Hi Minda,
It's been awhile since you asked this, but just in case you never got an answer, quilted postcards are pretty easy to make. A nice break from working on bed-sized, or even art quilts since they're only 4x6 inches.
Just like a regular quilt, you sandwich a filler between a pieced top layer and a simple back. Instead of batting, though, you use interfacing so it will be stiff enough to go through the mail.
Self-adhesive stamps stick to the fabric back just fine, and I've known people to just drop their finished piece in the mail as is. If there are buttons or embellishments on it, it may be better to get the postcard hand canceled and mail it in a clear envelope.
There are some great illustrated instructions on the web at:
http://debrichardson.com/blog/2005/09/26/how-to-make-a-fabric-postcard-debr-style/
and
http://dollmakersjourney.com/fabricpostcards.html
Here's a gallery of fun finished pieces in lots of different styles:
http://www.art2mail.com/gallery.php
Hope this helps! :D
Crystal