I would like to know how a pentium d, released 4 years ago is not that old, seeing as how its ancient in computer terms.
Just up till core 2 duo was released 2 years ago Pentium D was top intel performer.
A pentium D @ 3.6ghz should give you comparable performance as a 1.8ghz core 2 duo in games so it's not that far off as you think it is.
It's a dual core so it's not going to bottleneck as much as single core on games like COD4 that is optimized for dual core. Although it's not going to compete with a core 2 duo @ 3 ghz it's still adequate to game on.