vga cable Monitor hook up set up HELP

i bought a used xbox360 console that came with the vga cable. i can hook up the display to get picture but I can't hook up the sound to my set or generic brand **** speakers. I think the vga cable was supposed to come with a adaptor or something (it's 1st party btw) but the previous owner didn't give me one. I actually posted on the forums before and someone led me to these

http://www.radioshack.com/product/index.jsp?productId=2103225. I can hook the phono jacks from the vga cable but i'm not sure where to plug in the stereo 1/8" plug. My speakers have no plug like that.

is this even the right plug? or can someone point me to the right place