Throwing this in for PowerShell 2.0 and upwards:
Run New-EventLog
once to register the event source:
New-EventLog -LogName Application -Source MyApp
Then use Write-EventLog
to write to the log:
Write-EventLog
-LogName Application
-Source MyApp
-EntryType Error
-Message "Immunity to iocaine powder not detected, dying now"
-EventId 1