[July 16, 2007 UPDATE:] After downloading Nero 7 Ultra Edition Update I was able to upgrade my original dysfunctional Nero 7 Essentials. I tried to uninstall Nero 7 Essentials, but uninstallation failed. I had to use Windows Installer Cleanup Utility to get rid of Essentials first. The good thing was that after Essentials was gone, Ultra Edition upgrade found registration key of Essentials and used it to get installed. Naturally, after it was installed it still only had functionality of Essentials, not Ultra. Nero 7 Ultra came as a ridiculous 120+ MB download, with tons of junk, like ASK.com toolbar, so I had to spend time making sure it won't get installed. Funny, but help system is not included into the 120 MB download. To my surprise there was no "Burn DVD Files" option in Nero Start Smart, which used to be there since Nero 6. Fortunately, I found "Burn DVD Files" in the Nero Express UI itself. At this point I haven't burned any dual-layers, but single layer DVDs burned at 16x speed on my NEC 3550A drive just fine. Hopefully days of no decent software for DVD burning on Vista x64 are over.
Success: Nero 7 Essentials with Ultra Edition Update.
[END OF UPDATE]
Tried to burn Dual-Layer ISO image on Vista x64 with a few different pieces of software. These are the results:
Success: (with caveats) ImgBurn - does the job, but created a few dual-layer coasters, and almost invariably fails the burned disk verification at the end, even if disk is perfectly playable.
Failed: Nero 7 Essentials - filed to start after installation.
Failed: ISO Recorder V3 64 Bit - failed after finishing the first layer.
Failed: Active ISO Image File Burner - failed after finishing the first layer.