BIAB 2011.5 for Mac isn't a PowerPC application (nor is version 2009, 2010 or 2011). It's a native IntelMac app, and installs to Lion just as it did for Snow Leoparad and other OS's.

Versions prior to 2009 were PowerPC, so they would be no-go on Lion, because Rosetta is not included (or available) by Apple. https://discussions.apple.com/thread/3205007?start=0&tstart=0

If you run Lion, but still want to use an old version of Band-in-a-Box (pre 2009), then one of your only options is a dual-boot SnowLeopard/Lion
https://www.youtube.com/watch?v=MJhT3HAGog8&feature=youtu.be
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Have Fun!
Peter Gannon
PG Music Inc.