1. Type gpedit.msc in the Start Search box and hit Enter.
2. Click Continue when the UAC prompt appears.
3. Navigate to the following policy location:
Computer Configuration\Administrative Templates\Windows Components\Event Log Service
4. Look under Application, Security, Setup or System to configure settings for the log desired.
5. Enable the following policy setting:
Back up log automatically when full
Note that you should also disable the following policy if you are going to configure the above setting:
Retain old events
If you do this, then when the event log becomes full, the event log file is closed by Vista, renamed, and a new event log file is created.
Mitch Tulloch, MVP