Dopefish guided me through the process of being able to play on my PC LCD and using my headphones for sound via my sound card.
First used a HDMI to DVI adapter for the video and a RCA to Y cable.. or something like that. lol.. I forget what it's called.. but I wrote it down somewhere when I bought it.
I think it's mentioned in my thread when I asked if I could play XBOX 360 on my LCD.
Good luck.
BTW, save up for a 720p monitor. For some stupid reason, XBOX 360 doesn't support 16:10 resolutions and everything looks fuzzy sometimes. For example, in GTA IV, buildings in the background look distorted and in the day time when the sun is beaming, and HDR lighting is shining through, the shadows look horrible. I try not to pay attention to that though
P.S. 1680x1050 isn't 16:9

it's 16:10
1680 divided by 1050 = 1.6
If a width divided by a height gives you 1.6, then that's a 16:10 resolution. 16:9 resolutions are a little harder to determine since you get lots of decimal points.
1440 divided by 1.6 = 900
Works for any 16:10 resolution. This is a great tip for when creating custom resolutions and you want to keep the correct aspect ratio.
Anyway, sorry for kind of going off topic.