I am using Windows XP, now I want to install Mac OS X Lion (10.7). My problem is I want both operating systems. Is it possible? Will it be possible to use Mac OS X Lion (10.7) and XP simultaneously?
Questions that detail how to actually installation of OS X on non-Apple hardware are off topic due to the violation of the Apple EULA, but let's see if we can have a good general discussion of the issues and assume everyone is here to learn where the virtualization issues lie.
Using non-Apple hardware
Your only option is a hackint0sh.
Using a Mac computer
If you were using a Mac computer, you can use both operating systems:
There is a second way you can run on Windows hardware, although it pretty clearly seems in violation of the Apple EULA (at least to a non-laywer).
You can download and install VirtualBox. It will emulate the Mac OS X hardware and you can run Mac OS X on your Windows (this tutorial mentions Snow Leopard, but Lion will work as well).
Please note, although they say you can download a copy of Snow Leopard/Lion, this is illegal. You'll have to buy a legal copy of the installation disk in order to do this legally...