Just like to point out since Inflow, Plycon, and 2cooltek don't seem to know: there is no Pentium IV, only a Pentium 4.
When abbreviating Pentium !!! to P3, it's obvious why, to cut down on the number of characters to type. Calling a P4 a PIV is going in the wrong direction, and I'm not sure why people do it, other than some odd assumption that Intel continued the naming pattern and they didn't notice the change. (Remember, it was the Celeron2, not the Celeron II, if Intel officially named it that at all.)