Rogue Amoeba has released a new version of Audio Hijack Pro - v2.8 Preview 3. This update fixes a small bug with post-processing scripts and improves the reliability of hijacking from apps running under Rosetta.
Rogue Amoeba is still working to finish Leopard support for the Instant Hijack functionality. Instant Hijack enables the capture of audio from already-running applications, but when it's not available, Audio Hijack Pro simply needs to relaunch the source application. On Tiger, Audio Hijack Pro 2.8 Preview 3 is feature complete with plenty of updates and new features over 2.7.3.
An Audio Hijack Pro 2.8 final release, with Instant Hijack working on both Tiger and Leopard, will be available in the near future, but Preview 3 is now recommended for all users on OS X 10.4.0 through 10.5.1.