LGA775 belongs in the museum.
If want to spend much money on it, you are like spending money for nothing.
It is a different story if you plan to replace on lythe proc with second-handed Q6600, Q8200 or any other Qxxxx from eBay.
If you want to replace the mobo, get an after market cooler, get new proc, OC it, get new PSU, etc. etc. It is just not worth it anymore.