I missed this the other day, but Jeremy over at LinuxQuestions has details on the Dell Linux rollout. Nothing too surprising, fairly basic machines with well supported hardware. No proprietary media formats, so it seems like a fairly stock Ubuntu install. No Linux prices yet.
The top-end machine that will be in the initial offering is the XPS 410, which is $899+ with Windows on it. On the value end is the E520, starting at $369 (Windows price). It looks like the E1505 Notebook will also be offered, which is a fairly basic laptop at $699 (Windows price again).