Yes ma'am, I made my own invitations. You can see it here:
http://www.secondstarillustrations.com/invitation1.jpg
The left side was the front, the right side the inside. I've blocked out the RSVP address and phone number for the privacy of my parents hah =)
Anyway, here's what I suggest: find someone you know who has Adobe Photoshop or Illustrator, and knows how to use it. (These programs are expensive, so I wouldn't suggest buying them for the purpose, but you should probably be able to find a friend with them - specially if you have someone who's in the graphic design field.) I went about designing my invitations once I had decided on a "theme" and colors for my wedding - as you can see, my "theme" was butterflies (I had a live release after my ceremony) and my colors were coral and goldenrod. Keep it SIMPLE - simple is elegant. If you have one of the programs I mentioned above, you'll have access to lots of "premade" images/icons (my butterflies started as a pre-made butterfly icon that I copied and positioned and resized.) Also, you'll have lots of fonts to choose from. If you've never done this sort of thing yourself, you're really gonna need a friend handy who's familiar with the concepts of graphic design.
As far as producing the invitations, I recommend burning your images to a cd as JPEG files or PDFS (MAKE SURE the resolution is something high like 300, so that the printed image is pristine). Once you've got them to the correct size, make a separate file for the front, and the inside. Then, take the cd to something like a Kinko's in your area and tell them exactly what you need. They'll let you pick out the type and style of paper (I used a semi-hard slightly tan-colored paper - but stay in the neutral colors and don't stray far from white!)
If you need more help, or have some ideas you want me to "create" in photoshop and send back to you as JPEGS, feel free to email me at iownuga@gmail.com - my brother and I have been doing graphic design stuff for a couple years now (www.blueeclipsedesign.com) and I majored in scientific illustration in college, which included lots of graphic design classes. Anyway, I got married last year, and now I'm a navy wife living working part-time and have a lot of free time on my hands =) Good luck!