To look up Census Tract number by address
http://app.ffiec.gov/geocode/default.htm

Texas Department of Housing and Community Affairs (TDHCA)
www.tdhca.state.tx.us

IRS
www.irs.gov

Census tract reference maps
http://factfinder.census.gov/servlet/BasicFactsServlet

Capital Area Housing Finance Corp
http://www.cahfc.org

Austin Housing Finance Corp
http://www.ci.austin.tx.us/ahfc/first_homemap.htm