How can i install an external HD on my laptop

You need to put the HDD into an external enclosure or a hard drive dock such as one of these:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you buy an enclosure, make sure it's the right size for your drive - they come in different sizes for 3.5" desktop drives versus 2.5" laptop drives.

What you want to do is nor clear. It sound like you want to 1) Replace defective Hard Drive and 2) Do Data recovery on the defective one. If this is correct then replacing the defective one is straight foward. As for data recovery buying a hdd enclosure and puting the defective one in it and pluging it up to a working system is your best bet.... if you have lots of money then sending it out to a data recovery firm would be your next step.

Thanks, helpful answers, and indeed i want to do a DATA recovery on the defective one.

This is the easiest "no tools" solution:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thanks everyone, at the end i managed with a recovery tool to recover all the 650 GB in my crashed HD.