More than you need to know about the Democratic caucus system in Texas.
On March 4 2008 Texas Democrats will caucus at each precinct. At each precinct a minimum of 15% of the attendees must support a candidate for his/her representation to be viable. Delegates are chosen to go to the county or senate district convention.
At the county/senate district convention again 15% is required for viability. Precincts and precinct groupings select delegates to the state convention. Then "at-large" delegates are chosen by the nomination committee so that the proportion of each candidates delegates are reflected in the representation of the delegation. Even if a candidate is represented from precincts or precinct groups the candidate will not receive at-large delegates unless they are over 15% for the county/senate district convention as a whole. They will receive the precinct or precinct group delegates.
This is done again at the state convention being held in Austin June 6-7. The senate districts, again obeying the 15% viability rule, elect their delegates to the national convention. Each senate district has between 2 and 8 depending on Democratic votes in 2004 and 2006. The state convention also formalizes the "unpledged super delegates" based on political office or party committee membership. Then pledged party official and elected delegates are selected by proportion of candidates delegates attending the convention. Then "at large" delegates are chosen reflecting the proportion of the presidential candidates that signed into the party convention.
Note there are several levels where the 15% rule comes in play, at the precincts, at the precinct groups in the county/senate district conventions, at the county or senate district conventions as a whole, and at the state convention.
The Republican rules are somewhat similar but with a 20% viability rule.
Come out to caucus at 7:15 PM March 4th to really decide on the presidential candidates.