Triple Booting Xubuntu, Ubuntu and Windows

I'm an avid Xubuntu (Ubuntu + XFCE) user but I also dual boot with Windows XP. I originally created 3 partitions and wanted to use the empty one as a storage volume but now I want to install Ubuntu 12.04 LTS (the one with Unity) to do advanced testing and packaging. Ideally I would love to keep these two totally separate as I had problems in the past with conflicts between Unity and XFCE. This way I could wipe the Ubuntu w/ Unity installation if there are problems and really mess around with it.

My disk looks like this:

/dev/sda1 --> Windows XP /dev/sda2 -->

Disk /dev/sda: 200.0 GB, 200049647616 bytes
255 heads, 63 sectors/track, 24321 cylinders, total 390721968 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63    78139454    39069696    7  HPFS/NTFS/exFAT
/dev/sda2        78141440   156280831    39069696   83  Linux
/dev/sda3       156282878   386533375   115125249    5  Extended
/dev/sda4       386533376   390721535     2094080   82  Linux swap / Solaris
/dev/sda5       156282880   386533375   115125248   83  Linux

Keep each in it's own partition and totally separate and be able to select from each of the three systems from the GRUB boot menu...

sda1 ---> [Windows XP]
sda2 ---> [Ubuntu 12.04] "Unity"
sda3(4,5) --> [Xubuntu 12.02] "Primary XFCE"

What is the safest and easiest way to do this without messing my system up and requiring invasive activity?