They originally were losing $100 per box, but now they're selling the boxes for less. Sony isn't losing nearly so much because their box can be made for a lot less - Microsoft's is basically a PC.
The economics is, you bomb the box and make your money on royalties paid by the game programmers, but XBox has failed to generate enough developer interest, buecause the volume is poor.
Nontheless, Microsoft will continue with XBox and new versions of XBox because it's their entry point to take over home electronics, home entertainment, home communications and control of the appliances (universal plug-and-play). They are going to take horrifying loses for as long as it takes, or until they are defeated.