From script repository I did use in the past, VBscript which allows to clear EvenLog on Windows machine. I did use that on computers with Windows XP and Windows Server 2003. however, this script will work also on Windows 7 and Windows server 2008.

By default script clears EventLog on computer where script is executed. To clear logs on remote machine just modify variable strComputer and replace dot with name of the target machine.

Script will read all EvenLog files from machine and will go through them removing all events.

And here is script itself :

strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate, (Backup, Security)}!\\" _
& strComputer & "\root\cimv2")
Set colLogFiles = objWMIService.ExecQuery _
("Select * from Win32_NTEventLogFile")
For each objLogfile in colLogFiles