Well, it's nearly a year since this question was posted, so you've probably sorted it out or given up. But I'll post this anyway in case anyone else has the same question.
You can't edit video with NeroVision Express 3 SE. You need to upgrade to Nero Digital Pro. That installs NeroVision Express 3 and enables video editting.
You can download the upgrade from Nero here:
If you enter your Nero 6 serial number, it will just reinstall NeroVision Express 3 SE. You need a separate serial number, which you can purchase here:
(Please note, it would be illegal for you to use a serial number you found on the web.)