You need the lga775 intel MB, you will not find too many choices because it is the outdated MB.
If you can find like Gigabyte GA-G41MT-S2PT (G41 chipset), Intel DG41RQ, Intel DQ45EK (Q45 chipset), etc.
If you can't find the lga775 for the good price, then you think about to update the whole PC.