On the second page, there is a Customized Type Mappings table. First, you need to click the Add button. Next, click on the JDBC Type cell and enter the JDBC type (VARCHAR, CHAR etc) that you want to map. Click on thHibernate type and enter the Java type that the JDBC type should match to.
Hit Finish and that should take care of the rest.
Here is a table that you can refer to go get an idea on what Java Types the JDBC types should map to.
http://db.apache.org/ojb/docu/guides/jdbc-types.html