Is this Desktop compatible?
can i use this on a desktop?
also, can i use this as my main hd? as if i install it and install window in it.. will it work like that out of the box?
Yes, any Computer using a SATA connector will work. You can do a fresh install of your OS or clone the old drive to this one (assuming you are using 120GB or less of it) using apps available free online.
The size is only 2.5 inch so if you;re replacing a 3.5inch HDD you may need a holder/adapter to screw it into the bay. Like this:
http://www.bestbuy.com/site/crucial-ssd-install-kit/5457500.p?id=bb5457500&skuId=5457500
I just used some 2 sided tape to secure it in the case since the tower doesn't go anywhere. Hope this helps.