Expert: Rick Jackson - 1/27/2008

Question
one of the requirements given in the old testament for a messiah is that he must be from the house of david. since lineage follows the father in judaism (and yes, it did so predating jesus, i have recieved comments how jews made this up after, but histroical records, the old testament, and the talmud all show this not to be true), and a foster father does not establish lineage, how can jesus be a blood descendant from david on his father's side if his father is god?

Answer
Hi Paul.  Admittedly this is not a subject I am knowledgeable about, however I can share this explanation given in the Catholic Encyclopedia:

(a) If by virtue of Joseph's marriage with Mary, Jesus could be called the son of Joseph, he can for the same reason be called "son of David" (St. Augustine, On the Harmony of the Gospels, II, i, 2).

(b) Tradition tells us that Mary too was a descendant of David. According to Numbers 36:6-12, an only daughter had to marry within her own family so as to secure the right of inheritance. After St. Justin (Adv. Tryph. 100) and St. Ignatius (Letter to the Ephesians 18), the Fathers generally agree in maintaining Mary's Davidic descent, whether they knew this from an oral tradition or inferred it from Scripture, e.g. Romans 1:3; 2 Timothy 2:8. St. John Damascene (De fid. Orth., IV, 14) states that Mary's great-grandfather, Panther, was a brother of Mathat; her grandfather, Barpanther, was Heli's cousin; and her father, Joachim, was a cousin of Joseph, Heli's levirate son. Here Mathat has been substituted for Melchi, since the text used by St. John Damascene, Julius Africanus, St. Irenĉus, St. Ambrose, and St. Gregory of Nazianzus omitted the two generations separating Heli from Melchi. At any rate, tradition presents the Blessed Virgin as descending from David through Nathan.

Reference: http://www.newadvent.org/cathen/06410a.htm

That encyclopedia, though is almost 100 years old.  You might consider posting your question on the Biblical Archaeology forum where some may know of more recent textual finds that illuminate the genealogy better:
www.forum.bib-arch.info

Rick.