KiXtart Command-line Utilities - Eventlog
ClearEventLog
ClearEventLog is a FREEWARE Windows NT application that can clear the system, application, and security event logs via a simple command-line operation. It can clear them separately, or all at once.
LOGEVENT.EXE
The Log Event tool allows you to write information to the Windows NT Event log.
Syntax:
logevent [-m \\MACHINENAME] [-s SIWEF] [-c CategoryNumber] "Event Text"
Severity is one of (S)uccess, (I)nformation, (W)arning, (E)rror or (F)ailure.
Source: Windows NT Resource Kit