I already have a license for Windows XP and I have installed MS Virtual PC. Now I would like to install same Windows XP on virtual session. Does this violate licensing agreement? Is it possible?
Nope, the licence will not be valid if you are using a standard OEM, retail or upgrade package - You will need a new licence for use within the virtual machine.
If this is for testing and or development, you may be able to take a look at various VHD programs that Microsoft offer and find one that matches your needs. You simply download a few files and are ready to go.
Unless you have a site license key that allows you to install multiple copies using the same key, you have to buy a new license for each Windows virtual machine (VM) you want to run Windows XP on. Your license probably includes something similar to:
From the Windows XP SP2 Pro EULA.