hmmm... its an ISO file. Try to use Nero or other program (MagicISo, PowerISO) to open it and burn it. DO NOT burn it directly to the dvd, otherwise u'll just end tranferring it to the DVD. If all else fails, mounti t with Daemon Tools and burn an exact copy from the virtual drive to your dvd burner.
BTW, vista RC2 JUST (like 10 minutes ago, for the x64 version, 3 hours or so for x86) came online. If your a CPP member, which I assume you are, grab ithere
before MS takes it off.