We've obtained a copy
of the agreement on Karl Rove and Harriet Miers' testimony about the US Attorney firings, and it appears to answer some of our initial questions
Are any subjects off limits?
The scope of the interviews will be limited to: (1) facts relating to the evaluation of, decision to dismiss, or decision to replace the former U.S. Attorneys in question; the alleged decisions to retain certain U.S. Attorneys; and any allegations of selective prosecution related thereto; and (2) testimony or representations made by Department of Justice officials to Congress on the U.S. Attorneys matter. For the period beginning on March 9, 2007 (the date of the Committee's first written demand for information from the White House), interviews will not include the content of conversations involving: (i) Mr. Rove and members of the White House Counsel's office; or (ii) Ms. Miers and members of the White House Counsel's office. In the case of Mr. Rove, the interview also will include facts relating to the prosecution of Alabama governor Don Siegelman.
And when can Rove and Miers claim executive privilege?
As to official privileges, counsel will direct witnesses not to respond to questions only when questions relate to communications to or from the President or when questions are outside the scope of questioning set forth above.
You can see the whole thing here