Hi!
First off, the usual multiboot scenario doesn't seem convinient to me.The usual multiboot scenario is like the following:
1. Make two primary partitions
2. Install XP
3. Install Vista
4. Use Vista boot manager to choose the OS
I don't like this scenario because when deleting or formating XP partition you loose access to Vista partition.
The only acceptable scenario is the following:
1. Make two primary partitions
2. Using eg., Partition Magic, make the first partition (or second one, doesn't make the difference) active and the other one hidden
2. Install XP
2. Using eg., Partition Magic, make the other partition active and the first one hidden
3. Install Vista
4. Use third party boot manager to boot whatever OS you like. The third party boot manager automaticly sets the two partitions hidden/active.
This way you can have even three Os installed, each one on it's indepandent primary partition. Now, in case of anything you still have the access to one partition (or two part. if you installed three OS's)
I used this scenario with xp/win2000 installations and it worked great.
Now, my question is if this scenario is possible with Vista is installed.
I managed to do this using SPFDisk. But I installed its boot manager to floppy. Don't know if it would work if installed to MBR.
Any suggestion is welcome.

Visit TerabyteUnlimited.com & download their boot manager software. It is a 1 month full working trial version.

It can install in its own partition & will allow any number of partitions. So Installing a new OS or deleting a partition will not affect any other OS or your boot choice.

It has turned out to be the best investment I ever made.

BTW I have 6 + versions of Windows & 6 + versions of Linux installed & running on my pc.

I believe Vista ignores whether partitions are hidden or not. I'm not sure about XP but since you mentioned it worked with XP/2000, XP may not ignore hidden partitions.

Therefore, you may want to install Vista first to an active partition. Then use a third-party program to hide Vista partition and make the XP partition active. Then install XP. You might have to repair Vista boot up since XP will overwrite the MBR.

The only way you can boot the two OS's without using Vista's menu is to use Grub as explained in the Dual Booting Vista/XP with Grub here.

This method still relies on the boot manager (which is grub) to be on the active partition.

Even if you use a third-party boot manager, it still installs to the active partition or creates its own partition. In this case, if you lose the boot manager partition, then you can't boot either OS.

I have been using BootITNg (Bing) for nearly 3 years now.

I presently have 2 version of XP, 2 versions of 2k3 & TWO versions of Vista - Ultimate & Business - installed on my system apart from several versions of Linux. There is no interference from any OS with any other OS.

The way Bing does it is it maintains all the data in its own partition called EMBR. When ever you opt any specific OS to boot it presents a special Partition table to the OS - which always runs in memory. The way Vista would see areas used by other OS is as - "Unused Space"

You will never have to use Vista bootmanager. You also have th option of making other partitions visible/available to other OSes - up to 3 primaries & 1 extended - at your option.

There is one caveat though. You must never never use any other partitioning software when you have Bing installed.

Bing can create all kinds of partitions but cannot format them other than the standard fat & fat32 partitions. It will only mark thenmas such - ntfs, linux, linux swap or what have you. You have to let the installation software do that bit.

Most installations (except Linux) will overwrite your MBR. It is a simple matter to boot from Bing disk to reactivate itself. All your choices are once again available to you. I can assure you Neither Vista nor any other OS will ever be aware of existence of any other OS. Some Linux partitions are finicky when partitions for their installation are not formatted. It is a simple matter to boot live version of either DSL or Puppy Linux to format these partitions & install Linux.

Only time I Had problem with it was when Ububtu 6.06 trashed my entire Partition table & I almost lost my entire hard disk worth of data. Bing was able to undelete & restore every one of those partitions without loss of a single byte of data.

So what I do is ALWAYS create a fresh bootable CD/DVD from Any installation cd whatsoever by including BCDW 2.01 as cd/dvd boot manager & also including Bing + other diagnostic + partitioning/formatting software on it.

Try it, you will love it.

Are you sure, I hope at least the drive letter can then be changed using a letter towards the end of the alphabet. I tried that but the disk manager in Vista won't allow changing the drive letter of a XP partition , in XP I can change the drive letter of another system partition, no problem. I think in Vista MS makes multi boot a major pain on purpose forcing people to use Vista exclusively.

Here's another solution to booting independently: Boot Vista and XP Independently