Here's a small tip for those wanting to install Vista as second OS along with their XP on different partitions. You can install Vista either from within Windows XP or by booting directly from Vista DVD. Both behave differently. If you have decided to use first method, then XP and Vista will retain their drive letter, whatever OS you are in. That is to say, if you have XP installed in C partition and Vista installed D partition, then whatever OS you are in , both will be shown in their respective drives it has been installed , XP in C and Vista in D.
Now if you have installed Vista by directly booting from DVD, into say D partition, here in this way of install, whichever OS you are in each will be shown in C. To be clear, if you are in XP, it'll be shown as in C:, while if you are in Vista , it''ll also be shown as in C:. This will be useful to install programs which are hard coded to be installed on C drive. Also if one wants to remove Vista then all its related installed programs will be on one drive.
But this dual boot has some issue related to restore point, Vista restore points are deleted when booting into XP, while the XP restore points are not deleted when Vista is booted.
Also appropriate vol label can be given for each drive. But dont try to modify or change other OS volume label while in one OS.