I have a system:
dual core pentium d 915 currently running at 2.8GHz
with 2GB DDR2.

I wish to upgrade it to be used as an application server.
I wish to upgrade the processor and ram to 4GB.

Question1: Upgrade processor without changing board?
Is an intel quad core (core 2 quad aka C2Q) plug compatible with the current processor to replace it?

Both D915 and C2Q is on lga775.
D915 power are 1.2 to 1.3375V
whereas C2Q, depending on the model, are various between 0.85, 0.96, 1.16 lower threshold and between 1.5 to 1.3 upper threshold.

Question 1a:
In my former but obsolete career in semicon product engg, we tend to profile devices of the same design and manufacturing stream into different frequency performance correlated with different power supply voltages and then sell those similar processors but tested to different performance grades as different processor models. Is this the case with the power voltage variation among the C2Q models? That as long as my mother board provides a supply of 1.2 to 1.3 V, the power supply of the board is compatible for a C2Q processor?

Question 1b:
Are the 775 pinouts of D915 plug compatible with, directly corresponds to, the 775 pinouts of a C2Q?

Question 1c:
Are the source and drain currents/voltages that are suitable for the D915, also suitable for the C2Q?

Question 2:
The system has only 2 RAM slots occupied at 1GB DDR2 each.
Can I replace them with 2x2GB DDR2.
Are the pinouts of 1GB DDR2 compatible with pinouts of 2GB DDR2?
If in the future they made 4GB ddr2, would they be pin compatible with 1GB DDR2.
Does a mother board place any restrictions so that extra active pins beyond 1GB addresses are ignored and therefore I won't be able replaee the 1 GB DDR2 with 2GB DDR2 strips?

Or perhaps, I should replace the mother board?
If so, what is the lowest priced board for C2Q that would take 8GB?
If possible with builtin wireless.