In my experience Nanya are pretty descent chips.
Sometimes when you buy Kingston Value Ram the chip on the sticks are nanya sometimes its samsung etc...
It should run fine on your P4P800.
Asus P4P800DX, P4C 2.6ghz@3.25ghz, 2X512 OCZ PC4000 3-3-3-8, Leadtek FX5900@450/875, 2X30gig Raid0