Yeah, I got my 360 plugged into my monitor right now so I just press a button on the side and they swap from PC to 360, it is real nice =D only prob is my monitor is 16:10 and xbox just stretches the image from 16:9 to fit in, but I really dont notice at all, the image quality looks awesome, if I wasn't told that xbox didnt support 16:10 i wouldnt have known.
Yes you can, just get the right connector for it. My speakers actually came with one, that just converts the left right audio cables from an AV plug into a normal headphone jack thing, that you can just plug speakers in. They shouldn't be too hard to find in stores.