Not possible. That CPU only supports DDR2 memory.
Um, no. The LGA 775 platform has the memory controller on the northbridge, not on the CPU.
There are vastly more LGA 775 boards with DDR2 than DDR3 but DDR3 boards do exist. LGA 775 boards are hard enough to find as is though and DDR3 ones will be even harder to find. Additionally, you will see absolutely zero
performance improvement wise from going to DDR3 with that CPU.
Your best bet is to buy an LGA775 DDR2 motherboard and use your existing memory or buy a brand new computer.