The FB2.0.0.0 install is just as happy to work with FB1.5 structured
databases as with FB2.0 database. But if you really want two both
engines installed, I think there are some comments near the end of
the FB2.0.0.0 release notes

>
> Where can I find directions for getting FB 1.5 and FB 2.0 to coexist on
> the
> same pc?
>