I believe the early Intel Macs they're referring to are the Core Duo / Core Solo machines which were 32bit only. Everything after (including the Core 2 Duo etc....) is 64bit.
Yep. The ~5-year old Mini I have is 32bit Core (not2) Duo, so I guess won't take Lion. But it's happy sitting under the telly for the foreseeable...
I think the very first incarnation of MPBs are also affected.
Not aware any Mac Pros are tho'!