HOW TO DISABLE ACCESS LOG BUFFERING:

You can't--there's a LogBufferSize registry key that you can edit (the default value is 64k), but apparently you can't make it zero.

http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/22591eaf-682c-4835-af5a-5397fcdd9d39.mspx