I had the via epia m1000 1ghz cpu for a small media center, and this played almost everything i threw at it, every now and then, a dvd would start to stutter, but i'm talking like 2 dvd's out of hundreds that were tried.
CPU usage would be around 90% most of the time when playing a dvd/divx file though.
If you want to run windows update on it though, do it over night, it takes aaaaaages!