Eventlog

Hi,

    You can do this by two ways.
1. Log to EventViewer
2. Log to your own data base.

EventViewer:
  
       Logging data to event viewer which is provided by the operating system. Check this article for further information.

      http://support.microsoft.com/kb/307024

Logging to Database:

    This is kind of custom defined in which you can create your own table where you can log your error details.

   Log4Net is opensource library which is mainly developed for error logging.   Following site you could find a good example for beginners.
  
    http://www.dottostring.com/2008/11/5-how-to-use-log4net-logging-aspnet-application/


Regards,
raaj