|BeOS for Power Mac:
The BeOS for PowerPC generally works with otherwise BeOS Ready Systems which have been upgraded with a PowerPC 750 processor card, but that is not an officially supported configuration.
The BeOS Preview Release (1 or 2) is not compatible with any system using a PowerPC 750 processor, whether built-in or added as an upgrade.
As for NuBus-based systems upgraded with PowerPC 750 cards from Newer, or any other card vendor, the systems remain NuBus-based, and will not be supported, regardless of the processor inside. The BeOS does not support NuBus-based systems, period.