The process of filling vacancies in the U.S. House of Representatives is stated in the U.S. Constitution:
When vacancies happen in the Representation from any State, the Executive Authority thereof shall issue Writs of Election to fill such Vacancies.
(Art. I, § 2, cl. 4).
Assumption: The category "vacancy" includes "vacancy by natural death".
A vacancy has happened in the representation from Georgia due to the natural death of Representative Charles Norwood. Pursuant to Art. I, § 2, cl. 4, the executive authority of Georgia shall issue a writ of election to fill the vacancy.
The Georgia Constitution:
There shall be a Governor ....
(Art. V, § 1, ¶ 1).
The Governor of Georgia shall issue a writ of election to fill the vacancy.
The Official Code of Georgia:
... he Governor shall issue, within ten days after the occurrence of such vacancy, a writ of election to the Secretary of State for a special election to fill such vacancy, which election shall be held on the date named in the writ, which shall not be less than 30 days after its issuance.
(§ 21-2-543).
Therefore, within ten days after 13 February 2007 (presumably, excluding weekends and holidays) Governor Purdue has to select a date to hold the special election. That date must be at least 30 days after the date the selection is made.