Hello,
I've already answered your similar issue in http://www.gamesas.com/index.php?/topic/1288189-help-with-setting-border-line-to-0/. No need to start a new thread.
I'll repeat it here anyway.
Make sure you're editing the correct ini file. It'll be in (for Win7) User Name\My Documents\My Games\Oblivion folder. There should be no UAC issues in that folder preventing a save. If so, make sure you have Admin rights.
Do
NOT edit the oblivion_default.ini in the regular Oblivion install folder.