Windows XP only recognizes FAT16, FAT32, and NTFS partitions. If it is not one of these (such as ext3 or ReiserFS), it will report it as an "unknown partition."
Some manufactures put a special partition for restoring purposes. It might happen that windows will not recognize that partition but it will still work with properly. Also if you have Linux on your system windows will not recognize too...
Primary NTFS Partition.....
Volume
You have to create at least one more partition for Vista. If you install Vista on the partition where XP is installed Vista will delete XP. To avoid such problem you have to have one more partition. When you do that just start the Vista installation process from XP and choose just created partition for Vista.
The boot partition
Yes, you can but you have to install Windows 7 in another partition.
It is not possible to install any Operating System next to another on the same partition. To dual-boot Windows 7 and Windows XP, first install Windows 7, and while in the partition manager, delete all partitions and create one for Windows 7 and one for Windows XP. Then install Windows 7 to it's partition. Then install XP to it's partition. You should now be able to boot either Operating System. Note: You must install XP after Windows 7 as the Windows 7 installation wizard would want to upgrade XP. WARNING: This will erase all of the data on your hard drive. Be sure to back up all of your files before installing anything.
When you are getting ready to install the OS, either Windows 7 or Windows XP. It has an option to Format or Partition a hard drive. If you use the partition function you can decide how much you want to take out of the hard drive storage.
Set the primary partition containing Windows XP to active
Windows XP requires at least a 2GB partition for installation.
boot partition
Use your Ubuntu CD. Find a program called "GParted" or "Gnome Partition Editor". Click on your XP partition and click "Resize" and make it smaller. Then, do the same with your Ubuntu partition, and drag it until it fills the space left by XP.