Help Burning Full Length DVD as an ISO to a DL disc

Hey guys.

I have backed up some of my movies on my HD as ISOs using DVD decrypter. They are full length, and in between 6GB - 8GB. I have a NEC ND-6500A in my notebook, and some double layer memorex dvd Discs.

I am trying to simply copy the ISOs onto the DL disc verbatim. I want an exact replica. I have tried using DVD decrypter write ISO, and NERO express 6. Both programs won’t let me burn the ISOs, usually erroring by saying that its not possible to write that much data. I’m not sure if I haven’t put down a setting correctly telling the software that I do indeed have a DL burner and DL media, or if I simply need different software. All help appreciated. THanks.