Well, my configuration file looks like this:
Code:
<!-- properties -->
      <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
      <property name="connection.driver_class">NHibernate.Driver.OleDbDriver</property>
      <property name="dialect">NHibernate.Dialect.MsSql2000Dialect</property>
      <property name="connection.connection_string">
         Provider=Microsoft.Jet.OLEDB.4.0; 
         User ID=Admin; 
         Data Source=PathToYourMDBFile; 
         Mode=Share Deny None; 
         Extended Properties=; 
         Locale Identifier=1031; 
         Jet OLEDB:Registry Path=; 
         Jet OLEDB:Database Password=; 
         Jet OLEDB:Engine Type=5; 
         Jet OLEDB:Database Locking Mode=1; 
         Jet OLEDB:Global Partial Bulk Ops=2; 
         Jet OLEDB:Global Bulk Transactions=1; 
         Jet OLEDB:New Database Password=secret; 
         Jet OLEDB:Create System Database=False; 
         Jet OLEDB:Encrypt Database=True; 
         Jet OLEDB:Don't Copy Locale on Compact=False; 
         Jet OLEDB:Compact Without Replica Repair=False; 
         Jet OLEDB:SFP=False;
      </property>
      <property name="show_sql">true</property>
      <property name="use_outer_join">false</property>
      <property name="query.substitutions">true 1, false 0, yes 'Y', no 'N'</property>
Maybe you do not need all special parameters in the connection string, but in general it works in that way.