<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<!-- Others sections -->
<section name="log4net"
type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
</configSections>
<log4net>
<appender name="GeneralLog"
type="log4net.Appender.RollingFileAppender">
<file value="Logs.txt"/>
<appendToFile value="true"/>
<maximumFileSize value="100KB"/>
<rollingStyle value="Size"/>
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%d{HH:mm:ss} [%t] %-5p %c - %m%n"/>
</layout>
</appender>
<logger name="NHibernate.SQL"
additivity="false">
<level value="DEBUG" />
<appender-ref ref="GeneralLog" />
</logger>
</log4net>
</configuration>
and call
log4net.Config.XmlConfigurator.Configure();
from you application startup.
A more Official route.
Here is some HowTo from nhforge.org