Will it be legal if someone uses Windows XP pirated, when MS stopped selling and giving updates of it ?

Nah, only ever legal for one copy. If you decide to do it anyways, I'd recommend making a dual-boot with XP and your other operating system. I did that with my new laptop because I love XP and 7 has some gay issues (can't go full screen in DOS prompt, for example, annoys the heck out of me.. can't play/make old school DOS or BASIC games... yes, that's right, no more DOOM for me, haha.) Yet, I still wanted 7 around because my laptop was designed to run in 7 and XP drivers for this particular model are extremely difficult to obtain (as this model has never came with XP on it.) I tend to use XP for downloading, networking, and internet quite often cuz it always functions as planned. 7.. not so much. Networking is horrible in 7. Anywho, yeah, I'd recommend a dual boot!

Even if Microsoft stops updates, it would not be legal. Copyright stays in effect for over 20 years. Since XP is only going to be 10 years old, it's still copyrighted and protected.

Also, your legal copy of Windows XP is only good for that old laptop as it is an OEM version and non-transferable.

And why on earth would you want to download a new computer (presumably with Windows 7 installed on it) to an obsolete and unsupported OS? Windows 7 is awesome.

if you have the disk or the installer (got it legaly) then no it is not pirtated