hi,
The system attendant provides logging, monitoring and administrative functions for exchnage. one reason that it is getting so big could be because that it is set to never delete these files.
if you open up exchange administrator and select DOMAIN > SEREVER NAME > Configuration > servers > SERVER NAME then in the right hand pane double click the system attendant. this will show your properties, select "remove log files older than" and set to about 7 days. this should help
if you want any more help let me know.
russell