Let them date
Two. One for Windows XP and one for Windows Vista.
No
XP, if you can scratch Vista and go for Windows 7
Yes, this would work. Yes. XP has to be installed first though because Vista does not allow the dual boot with older operating systems being installed after Vista Bob!!!!!!!!!!!!!!
On a computer with both Windows Vista and either Windows XP or Windows Server 2003 installed, Windows XP or Windows Server 2003 deletes any existing System Restore points belonging to Windows Vista during boot. Microsoft confirms this issue but maintains that it is a fundamental function of the way XP works and cannot be changed. According to Microsoft, the solution is to install Windows Vista on a separate partition invisible to XP.
Yes. There is a process called Dual Booting, but it requires two hard drives. Just search for "how to dual boot windows vista and windows XP?".
Ideally, Windows XP should be installed first, although it is possible to do it Vista-first.
...with Windows XP Professional already installed on your computer. Windows Vista cannot be installed without Windows XP Professional installed first on your computer, it's the same with Windows 7; Windows' latest operating system (OS).
You should be able to as it will to it anyway. If there is no start up then just insert it into the XP OS and start from there.
No. Obviously, if you upgrade to Windows Vista, you will have Windows Vista.
windows Xp is better but Vista is slightly faster
You could use Boot Camp to make a dual-boot for Windows XP, Vista or 7 and Mac OS X. You can then install Insanequarium in Windows