I want to be able to dice which OS to run when I turn on my computer. I want to keep my original OS (Windows XP) Please help me!
1) You can repartition your hard disk. Keep XP on partition 1. Then install Ubuntu / Xuvuntu on partitions 2 and 3 and use GRUB as a boot loader.
2) Alternatively, install Ubuntu / Xubuntu in a virtual machine under Windows XP. Then no need to repartition your hard disk.
Option 2 is easy (e.g. using Virtualbox) and does not mess up your XP install.
Option 1 requires some skill. If you just want to "try" ubuntu to see how it looks/feels. go for option 2. Later you can then install ubuntu permanently using option 1 and still keep the XP available.