Ableton Live (Mac) supports VST2 and AU.
32 Lives 1.0 supports Audio Unit (32bit) to Audio Unit (64bit) only.
32 Lives 2.0 supports Audio Unit & VST2.
For Audio Unit support, please make sure you've turned on "Use Audio Units" under Ableton Live Preferences -> Plug-Ins.
For VST2 support, please make sure you've turned on "Use VST Plug-In" (system and/or custom folder).