Vista - Dual Boot Problem

Because of the curiosity factor involved in seeing how a x64 OS would respond
to the digital media apps that I run on my 64bit processor, I decided to
install Vista x64 on a spare 40GB PATA drive on my x86 XP SATA setup.

I installed the drive and then ran setup directly from the DVD during
startup (I did not boot into XP first.) During setup, in the graphic
presentation of the partitions available for installation, I notice that the
spare drive (listed in the second column) had some old data on it, so I
formatted it and then proceed with the install without incidence.

Upon restart of the machine, after updating some of the drivers, I noticed
that I booted directly into Vista without a boot menu showing a choice for a
previous windows installation. After another restart to confirm that I had
the SATA drive selected as the first boot device in the BIOS, I again went
directly into Vista. I then checked the Startup and Recovery settings under
the Advanced tab of the System Properties, and noticed that Windows Vista was
the only operating system listed. After another restart, I noticed that the
installation DVD was still in the drive, prompting me to strike any key for
setup, then booting straight into Vista instead of the boot menu or XP.
Thinking that the DVD had something to do with the drives being recognized, I
ejected it, then restarted and then booted directly to XP. In XP, the Vista
installation shows up as my G: drive. In Vista, the XP installation shows up
as the D: drive. The drive letter assignments don't bother me. What bothers
me is that the bootsector was installed on the wrong drive.

First of all, why would the DVD interrupt the normal boot process like that?
Second, how do I get the Vista bootsector installed on the primary boot
device, which holds the ntldr/boot.ini files for the XP installation? Can I
move the boot folder to that drive? I can't run bootsect.exe from the DVD,
because its not a Win32 app. VistaBootPro was no help, either.