So I go windows xp sp3, but I know it is required to be on windows 8 for windows phone. Now my pc is more or lesweak in specs, so I would like to install duo operating systems on same pc, how will that affect free version of unity? Will I be able to open it?
There shouldn’t be any problem. Sometimes i’ve got several versions of Unity (personal edition) installed at the same time with only one OS and i haven’t had any issues. So there shouldn’t be any with the second OS.
Since you would be required to partition your harddrives in order to do this, you would want to make sure there was room for the unity application on each partition. You then have to install Unity on each partition separately for each OS you wanted to develop on. The challenge here is that you would want to make sure that the versions installed were the same on each OS filesystem.
The article found here suggests that the unity projects themselves are transferable and you should be able to change them from either OS.
http://answers.unity3d.com/questions/554151/export-from-windows-to-mac.html
I have not tested this myself however, and personally would recommend sticking to 1 OS for your unity development.
You could easily use the other OS to test the builds though.