Disproving the christian (and muslim) god

[Huggy Bear]

The Old Testament makes no prediction that the Messiah would be born of a virgin woman,

You mean other than the obvious one?

Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. - Isaiah 7:14

How about this one:

And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel. - Genesis 3:15

Here God is speaking to the serpent and he mentions the seed of the woman, normally women do not have seed, the seed comes from the man. God gave the woman a seed, which was Jesus Christ through the virgin birth.

be crucified for our sins,

But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed. - Isaiah 53:5

and then rise from the dead three days later.

For thou wilt not leave my soul in hell; neither wilt thou suffer thine Holy One to see corruption. - Psalm 16:10

In other words he'd raise hum up before his body started to decay, which is within 72 hours (3 days).

If you don't believe me, again, ask the Jews. They would know the Tanakh better than you do.

Who exactly do you thing wrote the New Testament?