As expected, Mac OS X 10.7 Lion will require an Intel Core 2 Duo processor (or better, such as the i3/5/7 series or Xeon chips) and 2 GB of RAM for a compliant install when it ships this summer. This is consistent with the requirements from earlier builds of the OS.
Judging by our Twitter inquiries, however, there is a good bit of confusion over the difference between "Core 2 Duo" (which is supported) and "Core Duo" (which is not). Here's the simple rule: Did you purchase your Mac (new) after December
2007 2006? It's probably OK for Lion, although it might need more RAM.
Core 2 Duo processors have been used in the Mac line since late 2006, and powered most consumer Macs prior to the introduction of the Core 'i' MacBook Pro models last year (except for the Xeon and successor CPUs in the Mac Pro and XServe). Core Duo and Core Solo chips, on the other hand, were only used in the first-generation Intel Macs (MacBook/MacBook Pro, iMac and Mac mini), and were not used at all after 2006. Even the low-power first generation MacBook Air from 2008 used a Core 2 Duo, and all MacBook Air models shipped with at least 2 GB of RAM.
Hope that helps! We'll have more details on "what Mac owners need to know about Lion" later today.