WARNING! Do NOT install XP after you've installed Vista 64. I did that, and it so completely screwed up my system I went through almost 2 months of on again/off again problems.
If you want to dual boot, so a techie told me, you must first install an older OS (XP) on a partition or even separate hard drive, then install your Vista 64.
I installed XP after Vista, big no-no.
Even now, after 7 installs of Vista, and after installing XP first, and with Vista and XP installed on separate hard drives (both SATA), (my rig: 8GB memory, Quad 6600 cpu, Asus P5W DH Deluxe), and even after I installed each with the other hard drive physically unplugged, I have boot record corruption errors ("BOOTMGR missing") with Vista.
The two OSs just don't seem to like each other on my system, even after I set up each system completely independent of the other.
Plus all this clouded another issue which I just discovered...a failing IDE drive.
The Vista boot problem happens when I select the XP hard drive in Bios as normal (I don't use a dual boot set up or program), boot up on XP, and use it for however long I want to without problems. But when I boot up the next time, select the Vista hard drive in Bios, and try to boot, I get the BOOTMGR error.
Popping the Vista install disk into the drive, rebooting from that, then doing a startup repair, gets me back into Vista...but it takes at least 20 minutes to do that.
Not worth the hassle.
I'm looking for some software solution that will allow me to dual boot without all this hassle, and without having to go into bios each time. But after all I've been through, and losing about 6 weeks worth of working time, I'd caution you to make sure you know what you're doing and above all, install XP first.
Because it seems both XP and Vista write some garbage on the other's master boot record whether you like it or not, which messes things up.