Connecting a 360 to PC speakers

[BigManBill]

Well I have two questions. I currently have a crappy little 2 stereo speaker setup that has a 3.5mm jack input. I'm getting a new moniter to play my 360 on and want to know what is the best way to connect it to my current speaker setup. I am assuming a converter for the two scart audio jack thingys on the 360's cable to turn it into a single 3.5mm (I will be buying a TV moniter so will be using the component HD cable). My other question is how to get surround sound. Say if I got a Logitech G51 5.1 system or similar, how would I go about connecting a 360 to it (and a PC as well preferably without needing to switch the cables) to get 5.1 surround sound. When it comes to anything to audio past the basics I have no idea. Also, if it matters I only have the onboard 5.1 Realtek in my PC, and no other audio equipment in my room other than the crappy two channel speakers. What connectors and equipment would I need to get 5.1 sound to a 5.1 computer speaker system? Thanks.