I checked out the BestPractice software but it appears to be solely Windows based so not suitable for me with a Mac. I've previously looked for software that can take out the lead guitar and whilst some I've tried can mute it to a degree, usually the process degrades other instruments in the process as it inevitably cuts into similar frequencies of those instruments, typically producing a swirly wishy-washy effect on rhythm guitars etc.
For simply slowing down tunes in order to hear the lead parts more easily, try Riffmaster Pro (they do a 10 day trial demo - think they do a PC version too) just to hear the quality difference as some software that does this can also lead to very weird warbles and swirls in the slowed down versions whereas this software shows no such artefacts with everything remaining crystal clear and pure - it also has the same facility to isolate and subdue 'vocals' which seems to work equally well on guitar. There's a slider to adjust the effect but it can only subdue the lead and not eliminate it entirely.
Cheers,
Martyn
