Linux Ubuntu is the free operating system.Just download the ISO image file and burn it to the blank CD disk.
As for the partitions,trust me you do NOT need more then 2.Just split your HDD on 2 same size partitions.Since now you have 6 partitions and all your documents are spread all the way on them,sort them nice and put them all in "Other partitions" folder on the external HDD as I told you.
How to delete all the partitions is also very easy.Just boot your computer with the XP Home CD disk and when you get to the screen with the partitions,just follow the instructions witten on the screen.For example if you want to delete all the partitions,you will need to delete them one by one all until you have deleted them all and have ONLY the UNPARTITIONED SPACE.So you will use the third option called "
To delete the selected partition, press D.".Take a look at the image bellow:
http://www.theeldergeek.com/images/XP Pro Setup Graphic/FF.gif
Now you need to create 2 new partitions.C: partition and D: partition.To do that,AGAIN follow the instructions written on the screen.So now you will use the second option called "
To create the partition in the unpartitioned space, press C.".After you have presses C button on your keyboard,you will need to write the size for your new first C: partition in megabytes (MB).Here is the image:
http://www.build-your-own-computer.net/image-files/windows-xp-install-07.gif
So for your first C: partition size write "204800" MB.That is 200 GB.Now press the ENTER button on your keyboard to create the first C: partition.Now AGAIN press "C" letter button on your keyboard.Now you will need to again write the number in megabytes (MB) for the size of your second D: partition.So delete the current number,write numbers 9 as much as you can and press the ENTER button on your keyboard.After that all the numbers 9 will be reduced to the number in MB which is the biggest size you can use for the second D: partition.So after that again press the ENTER button on your keyboard.
Now you finally have C: and D: partitions created and they are both the same size.Maybe few megabytes (MB) difference,but nothing really important to worry about.Now select the C: partition and press the ENTER button on your keyboard and wait for few seconds until the BOOT SECTOR (MBR) is created.After that you will need to choose what file system you want to use for your Windows installation.Simply select "
Format this partition using the NTFS file system" and then press the ENTER button on your keyboard.
As for the rest,just follow my instructions written above.
Cheers!