I've currently running my overclocked e4500 to a very stable 2.9 Ghz ( w/ vcore at 1.26 to 1.28) on the P5N-D so you your e4600 should easily OC to a stable 3.2 Ghz.
I use the Artic Cooling Freezer Pro 7.
Looping tests of 3dMark06 and Prime95 for about an hour, both cores will go to 62 C and vcore stays at 1.28. You should be getting similar results as far as temps and vcore.
In the BIOS:
Disable the Qfan profile so your cooler fan will run full speed as you OC.
Unlink the memory clock mode.
Set the QDR to 1066.
Leave CPU volts on Auto (for now).http://www.youtube.com/watch?v=KtcFNcpcnQY
If you post and run your tests and its stable, you're good to go at 3.2 Ghz! Monitor your temps. Your vcore should be near 1.28 or lower.