1.
Your copy of XP is bootable. If you don't have a real one, try reading before stealing - the procedures are well documented.
2.
Just throw it in and it will take you to the correct steps on its own. If the computer is really old, you might have to force cd boot in bios - look for boot order options.
3.
Have a friend around that knows how to do this. It's basic knowledge, you do know someone who is capable.