Depending on when Congressman DeLay resigns and when Governor Perry calls the special election, potentially (though unlikely, as both would probably choose dates so that an election would happen first) the GOP nominee for November could be picked before the special election is held. Or, it's also possible that the district precinct chairs might decide that they don't like whoever wins the special election, and decide to nominate someone else to face Nick Lampson in November.
Here is a more thorough explanation of the process.
Full text of the statute:
Section 171.054. Committee Composition: District Situated in More Than One County; First MeetingTex. Elec. Code Sec. 171.054.
(a) The district executive committee for a district situated in more than one county consists of:
(1) the county chair of each county that is wholly situated in the district; and
(2) one precinct chair from each county that is only partly situated in the district, elected by and from among the precinct chairs of the precincts in that part of the county.
(b) Except as provided by Subsection (c), the county chair shall call a meeting to convene at any time after the precinct chairs take office to elect the precinct chair who is to serve on a district executive committee. The county chair shall notify the appropriate precinct chairs in advance of the meeting of its time, place, and purpose. Not later than the third day after the date the district executive committee member is elected, the county chair shall deliver to the state chair written notice of the name and address of the person elected.
(c) If a vacancy exists in the office of precinct chair on a senatorial district executive committee immediately before the date for conducting the regular drawing for a place on the general primary ballot, the appropriate precinct chairs shall convene on that date at the hour and place specified by the county chair to elect that officer.
(d) The members of a district executive committee shall elect a chair at the committee's first meeting from among the committee membership.
(e) The state chair shall call the first meeting of the district executive committee and shall notify each committee member in advance of the meeting of its time, place, and purpose.
I assume that wholly situated means that every member of that county is within the district. That isn't the case here. Therefore, the GOP nominee will be determined by the following process:
1. The GOP County Chair in Harris, Fort Bend, Galveston and Brazoria will call a meeting of the precinct chairs of that district.
2. Each county's precinct chairs will elect one precinct chair
3. Those four precinct chairs (one each from Fort Bend, Harris, Brazoria, and Galveston) will meet and determine who represents the GOP on the ballot in November against Nick Lampson.
4. If this process is not followed, then the state GOP committee (SREC) will decide on the nominee.
I'm fairly confident in that legal analysis (standard disclaimers apply: I'm not a lawyer, I'm not your lawyer, I barely even play a lawyer on TV), but it was very quickly done and I'm not an expert in the field. There are more angles I'd check if I were doing it for real. Moreover, I was up all night working on a brief on criminal confession in Texas. I was too tired to think about four hours ago. And then tonight I ended up analyzing election law. Could my life be any more exciting?
Also, memo to Texas legislators: that election code could be much clearer. I could be available in the next general session to help fix that. Heh.