Is Intel planning on calling Penryn Core 3 Duo or something?
No, Penryn is a shrink of Core 2 from 65nm to 45nm.
Core 3 will be 45nm, come out end of 08 /start of 09 and are codenamed Nehalem.
The next is Westmere, a shrink of Core 3 to 32nm
The next year, then 32nm Core 4 or whatever its called, codenamed Sandy Bridge.