How do I install a second version of the same OS on my PC. I need to install a second copy of xp pro on my PC so as I can access the files in my docs. I did this on a previous machine, but do not know exactly what I did. Please help.

Are you already running xp pro at this time? What OS do you have installed?

I have xp pro on machine, but cannot boot up, even in safe mode as I am getting blue screen.

Do you have friends that work on computers? Maybe one has a boot disk you can borrow and go in and repair what's wrong.

Either that or use a Linux Live CD, get all your data off and rebuild from there.
I have had great experience with Slax: your pocket operating system (http://www.slax.org/) simply burn to a CD and run from there.
Works a treat.

The BSoD could be anything and installing a second OS on the same hardware may lead to the same issue.