circumstances: vista-32 on 64-bit machine [Intel DG965RY mobo; Intel E6400 processor]. c:\250GB HDD holds vista-32, d:\500GB HDD vacant (although possibly automatically formatted when integrated.)

i want to install unix and linux on the d:\. i want to be able to move between the os's at run-time. i will also install GCC.

what is the best strategy to accomplish this? does vm figure into this? i will need you to express details, such as where to install Xen or Grub (c:\ or d:\), and what unintended consequences i might encounter (such as invoking the ire of resident vista -- i want to avoid a vista reinstall).

If you use a Virtual machine management layer you don't need Grub because each guest system you install into a virtual machine you don't install its boot loader because it the the host that get booted.

Grub will be useful to you if you boot each system individually so that every one resides in a partition and every partition has a boot sector where a boot loader can get inside.

A Host running VM is just one operating system. Guest systems are effectively just large files inside the host.

You cam mix them of course but there is no limit on the number of combinations.

Another possibility would be to use CoLinux as the VM to run Linux applications under Vista. Since its a cooperative VM (unlike VMware, plex86, Virtual PC, Xen etc. which virtualize the resources) you could run Linux applications at essentially native speed and be able to copy/paste between Windows and Linux applications, access the Windows files without having to create a file share etc.

http://www.colinux.org/
http://en.wikipedia.org/wiki/CoLinux
http://roth.textdriven.com/other/colinux/guide.php

http://ubuntuforums.org/showthread.php?t=81444 describes how to use Ubuntu with CoLinux if it doesn't have the features you want.

Personally I dual boot XP and Ubuntu with GRUB. I installed XP first to avoid any sideffects, leaving half of my 160GB disk unpartitioned. I then installed Ubuntu , using the setup programs partition editor to create several partitions for it. It replaced the windows boot manager with GRUB. I burned a copy of SuperGrub and SystemRescueCD beforehand as a precaution in case I ever ran into boot problems.

http://supergrub.forjamari.linex.org/
http://www.sysresccd.org/Main_Page

I would try, if i were you, to bring Vista to life inside a Virtual Machine, although you'll have to reinstall the product, you will forever be able to copy it with you to a new Linux installation if you need to do that. Vista would be completely and perfectly backuppable, and as we all know Linux is always an easier install .