Is it possible to have one MOSS Farm with two Database servers?
Yes, you can use multiple SQL Server database instances to host a single farm's databases. I've seen customers who separate out content databases (collab sites, MySites) to an instance separate from the one hosting their config database, SSP databases, etc.
You can even split content databases across instances as well.
It basically comes down to specifying the proper server and instance name when creating the database.