The rumor mill was spot on, it seems. An Eee Box B203 nettop has quietly appeared on Asus' website, and this model has a Celeron processor instead of the Atom that powers other diminutive desktops in the same lineup.
The Celeron 220 includes one 1.2GHz core with a 533MHz front-side bus and 512KB of cache, and Intel has based it off the same architecture as 65nm Core 2 Duos. This chip does have a lower clock speed and a higher TDP than the Atom 230, but because it has out-of-order execution and some of the Core 2 series' perks, it likely performs better.
Processor differences aside, the Eee Box B203 looks a whole lot like the B202 system we reviewed a while back. Asus puts in a 945GC chipset, up to 2GB of RAM, up to 160GB of mechanical storage, Gigabit Ethernet, and 802.11n Wi-Fi. Supposedly, the company went with a Celeron as a cost-cutting measure: this nettop may end up costing only $240, which would make it roughly $60 cheaper than the Eee Box B202.