Go to Radio Shack and tell them you want a 3.5mm plug to RCA adapter cable. It will have a 3.5mm headphone plug on one end and 2 RCA style plugs on the other end (one red and one white). I think you can also get them at Wal-Mart\Target. You shouldn't pay more than like $10 for it. Don't get the iPod Monster Cable one. They are like $30 and not worth it. So don't let the sales people talk you into that. The cheapo kind will work just as well.
well depending the kinda stereo u have u wont need that at all.. i have an rca home theatre system with usb option, and i just used the usb cord and connected it to the heaad unit, then my phone asked for my password, i put it in then the player says loading then bam.. u got your own juke box, and u can skip songs and stop and pause from your remote.. its pretty bad ***.. i love this phone lol
good luck!