I don't think you can make jpg or wmf files "Transparent"
I found several articles and software to make "Gif" files
Transparent, but it appears they can be used for Web Pages Only.
I tried several of the conversion programs, but couldn't get the converted "Gif's" to import to a CD Label Program as an image file.
You can search the Web"
"How to make jpg transparent"
"How to make jpg transparent and software"
"How to make gif transparent"
"How to make gif transparent and software"
THE CD+G ZIP FILE IN THE ABOVE MESSAGE, COMPACT DISC CD+G LOGO WILL WORK ON A WHITE LABEL BACKGROUND
Here's the links I found them at:
http://www.cdplant.se/eng/logotypereng.htm
http://www.cdman.com/graphics/disc_designing/logos.html
http://www.effectuality.ca/logos_art.shtml
http://www.u-m-l.com/logocdg.htm
http://www.gnscd.com/cdlogo.htm