This post could go under either software or hardware, because it’s about software that will affect your hardware. A lot of composers make use of older machines as “farm” computers for overflow sample libraries. I do.
If you use an older MAC, Mountain Lion is a problem. It looks like anything older than “mid 2007” is history. These are the units that Mountain Lion will support:
iMac (Mid 2007 or newer) MacBook (Late 2008 Aluminum, or Early 2009 or newer) MacBook Pro (Mid/Late 2007 or newer) Xserve (Early 2009)
MacBook Air (Late 2008 or newer) Mac mini (Early 2009 or newer) Mac Pro (Early 2008 or newer)