Is there only one partition on the 320 drive? You can partition the 320 drive to have two or more partitions. Install Xp on one partition and then install Kubuntu (via Kubuntu Live (Desktop CD)) on the other partition. Once Kubuntu is installed use the Linuxmce CDs to install LinuxMCE. Be sure not to use the LinuxMCE DVDs because that will erase your entire drive.
LinuxMCE CDs to use
Note. If you only have one partition on the 320 drive, you probably will have to repartition the entire drive, o make sure you back up your data. I just gave a quick overview that you can accomplish what you want to do, but I'm sure there is more info and details out there. When creating the partition for any operating system, make sure you pay attention to disk space requirements.