Hai,
First, try the speaker-to-line-in as mentioned by others.
If that doesn't work satisfactorily, you might consider
trying an attenuating dubbing cord from Radio Shack,
going to the mic in.
Some say to attenuate when going from headphone to line in.
I don't know the numbers, but you can try it.
At RadioShack.com, the cords are $3.99.
Search for "Attenuating", or for part numbers 42-2461 and 42-2152.
The differences are length and plugs.
They are mono, so you will need to buy other cables, or save money
by cutting up old stereo cables and making what you need,
assuming you are connecting to or from stereo jacks.
Don't insert mono plugs into stereo jacks.
You MAY be able to find a knowledgeable person at a Radio Shack store,
someone who knows more than how to sell cell phones and satellite dishes.
Here are some links that may help with the explanation:
http://k-lug.org/pipermail/klug/2003-May/007162.html
http://www.w5bbr.com/soundbd.html
http://www.qsl.net/wm2u/interface.html
http://www.storm.ca/~ve3iay/hookups.html
Maybe you will want to make your own attenuating interface
after reading these sites. <g>
Luck to you,
Rick