Re: bbPress 1.0 alpha
Same database or same tables within the database? Same database, sure, just use a different table prefix, like bbalpha_ or something.
For the same tables, I would need to look at the schema changes between 0.9 and 1.0, but I *believe* there are changes, which means it would not work to use the same exact tables.
edit: _ck_ beat me to it