From Apple's iDVD site, in case any of you missed it:
"DVD Now Supports
Double-Layer DVDs
The latest models of the Power Mac G5 include the new 16x SuperDrive featuring support for the burning of double-layer optical media DVD+R DL discs. And iDVD 5, version 5.0.1, already takes advantage of the drives new capabilities, letting you burn projects requiring up to 4 hours of video on discs virtually double the size of single-layer DVDs."
"DVD Now Supports
Double-Layer DVDs
The latest models of the Power Mac G5 include the new 16x SuperDrive featuring support for the burning of double-layer optical media DVD+R DL discs. And iDVD 5, version 5.0.1, already takes advantage of the drives new capabilities, letting you burn projects requiring up to 4 hours of video on discs virtually double the size of single-layer DVDs."