Power from car stereo to portable speaker

Odd question:

I bought 2 basic walkman speakers that i want to plug my ipod in. They will be fitted in my armrest but I also need a 9V power source (the speakers have accept a plug that i want to cut and connect to my car stereo.)

I am willing to pull the cables out of the back of my car stereo, cut them and attach the proper ones to the portable speakers. Any simple tips you can provide me?

Thanks 

Oopps,

all this will be hapenning in a "1991 Oldsmobile Regency Elite ninety eight"

Why do you want to do this, is it so you'll have sound from your iPod in your car?  If so, you could use an FM modulator instead so it will play through your car's existing speakers.