Before you can connect a database server with instantOLAP or any other Java application, you need a to install a matching database driver. For Java systems, you will need a driver which implements the Java JDBC standard and almost all database vendors provide a JDBC driver for their product.
Because of copyright reasons, only a few drivers are included in the instantOLAP standard distribution (an open source driver for Sybase and Microsoft SQL-Server and a second driver for HSQLDB databases). For all other database servers, you can find the driver in the internet. This is a list of the common database servers and some internet addresses where to find the driver.