Windows 2000 O/S, Sql Server 2000 Enterprise Edition. Will I receive better performance with SQL server running on 2nd server rather than having Baan and SQL Server on the same platform?

In either case the database(s) will be on a seperate HP SAN.

The most common case is to run SQL server and Windows on the same box. I would have thought that so long as you have enough memory and CPU it will be faster than a network transfer. As always it depends on how you are using Baan, and how large your DB is.