From the official "Idol" press release, here's the explanation of the save system:
Tonight, AMERICAN IDOL also announced a new twist in the competition: the Judges’ Save. Up until only five finalists remain, the judges – if they unanimously agree – have the option to save from elimination the finalist receiving the lowest number of votes. The judges do not have to save a finalist during the competition. However, if they choose to use the Judges’ Save, they may only do so once during the season. The following week, the two finalists receiving the lowest number of votes will be eliminated.
And next week brings country songs, with Randy Travis as mentor. From "Idol":
On Tuesday, March 17 (8:00-10:00 PM ET live/PT tape-delayed), the Top 11 finalists (Kris Allen, Megan Joy Corkrey, Anoop Desai, Matt Giraud, Danny Gokey, Alexis Grace, Allison Iraheta, Adam Lambert, Scott MacIntyre, Lil Rounds and Michael Sarver) will return to the IDOL stage and perform songs popularized by members of The Grand Ole Opry. In addition, country music superstar Randy Travis joins the Idols as the first mentor of the season.
Tune in the following night Wednesday, March 18 (9:00-10:00 PM ET live/PT tape-delayed) to see if the judges use their save or if America sends another finalist home. Also, Randy Travis and Carrie Underwood will sing “I Told You So” (previously a hit for Travis and now a hit single for Underwood), and Brad Paisley will perform his new single, “Then."
UPDATE: You can find a list of the current Opry members here. With people like Garth Brooks, Carrie Underwood, Lorrie Morgan and Travis Tritt on the list, it looks as if there will be plenty of leeway for the contestants -- although I am sure the show will also have some generous definitions of what qualifies.