I've spent quite a few days trying to install Win 7 in a dual boot enviroment with an existing Vista operating system. Vista came pre-installed on a large SATA HD that I reconfigured into 2 partitions (Vista on the 1st). Unfortunately, the OEM cabled the drive to one of the middle sequenced of 6 SATA connectors on the motherboard. I added another SATA HD to one of the lower ordered motherboard connectors. Selecting the Vista drive to boot 1st in the BIOS works fine for Vista, but this kind of configuration doesn't work when adding Win7. Win7 will install a "boot" folder on the lowest ordered HD (say HDD 0). Win7 boots fine from the installation DVD, but will only boot to Vista without the DVD. The boot loader just doesn't see Win7.

Re-ordering the SATA HD's connectors on the motherboard so the boot drive is recognized 1st, with Vista on the 1st partition & then installing Win7 on the 2nd partition finally got it all working just fine. BCD editors & boot loaders now work also.