Hi Luftyman,
"step by step because I am a novice for computer system" so READ more to get the info you need!
Begin here and read at least 1 to 6!! "
http://www.plop.at/en/bootmanager.html"
If you have important data back it up!!!
There are different ways to do what you want.
You can burn an ISO image to a CD or if your USB is bootable copy plop to usb(more risky as HD's may be swapped so be sure to install on the right one) .
Do you already have operating systems installed?
Dit you make the partitions 1,2 And 3??
After installing a windows the MBR is overwritten , this is normal and only preventing plop from load, run installer from plop to enable again.
If one windows may not see the other you must use the Clear functon op plop , Be sure to first SAVE the partitions in the bootmanager.
And keep in mind that there is data in the space windows is saying not used .
Warning windows COUNTS partitions so if you have the partitions 1,2,3 and they all work and you clear partition1 partition2 will NOT work without change boot.ini of XP.
So read more and try
Regards , Jan