In Commerce Server 2007 Staging (CSS) the event logging will retain 3 days worth of event and project data by default. The number of days can be adjusted from 1 to 999 by manually editing the appropriate registry value.
To adjust the value follow these steps:
Open Regedit.exe and expand to HKEY_LOCAL_MACHINE\Software\Microsoft\CSS\EventLogging\CSSLocalEvents
Right click on the value 'EventLifetime' and select Modify.
Change Base to Decimal and then enter the Value data (number of days) you want.
Select OK to save the value.
After saving the value you will need to restart the Commerce Server Staing service so that the new value will be used.