What makes my friends MBP extremely slow?

[poobear]

Hi everyone,
My friend has a MBP (2010 or 2011 model, 4GB ram) that is extremely slow. I ereased and re-installed OS X (10.8), which made it a little bit better but I still see the beach ball all the time.
I know of hard drives getting slow sometimes before they die. I guess that ram memory can also be slow if they are defect? And I have no idea about processor being slow when defect.
There has to be a hardware problem somewhere, but I'd like to know what it is before I buy her new part(s).
What are the recommended software to find the bottleneck? Any popular harddrive/ram/cpu benchmark softwares that I can try out quickly and compare with other peoples results?
I've heard of (but never used) Xbench, but the results website (http://db.xbench.com) can't be reached, and by looking at the bottom of the website http://xbench.com of everything it measures I get headache, I don't know which of all the tests I should look at.

I'm completely new to all the benchmarking, just wanna find the defect part in a system.

Thanks!