i want to learn linux ubuntu and i have decided that i ll using it under microsoft environment … so MS virtual pc came to my mind … [/quote]if you want to run Linux in a virtual environment, then use VirtualBox instead. Linux support is much better.
You might also have a look at the wubi installer which is aboard on recent Ubuntu versions. You then install Ubuntu under Windows like any other Windows application. See here: http://wubi-installer.org and especially here: http://wubi-installer.org/faq.php
Much faster than Ubuntu in a virtual machine, but you need to reboot to switch to Ubuntu.