Hey, get one of these:http://www.amazon.com/Stereo-Optical-Audio-Cable-Xbox/dp/B001H847Q2/ref=sr_1_22?s=electronics&ie=UTF8&qid=1302050930&sr=1-22
It costs much less than the converter box that you're looking at and it serves the same purpose.
I've got one that's just like it, and I played on my 1280x1024 monitor for the longest time. It looks waaaaaaay better than your standard-def TV. It's not as good as a nice flatscreen 1080p TV, but it only costs 1/100 as much to just buy a cable, so it's a fair tradeoff.
Bottom line: it's like having an HDTV that's the same aspect ratio as an older TV. It's not widescreen, but the picture is much, much clearer.
Oh, and make sure you're getting an official cable from Microsoft, a lot of the lookalikes are made much more cheaply. You're better off getting a good Microsoft cable for $15 more than having a knockoff that doesn't work.
Hope this helps.