I am currently using windows XP2. For practice purpose i want to use UNIX shell scripting. Without installing UNIX OS how can i use the UNIX shell scripting?

You should be able to download the Unix Services for Windows, version 3.5, from Microsoft (free). There are other shell emulators that are available for Windows, which would allow you to use Unix type shell scripting without installing any additional OS.

Your question about "virtual UNIX" is unclear ..