Thanks for all your replies. Currently the x64 version runs good. I'd give it 70/100. The RAM is generally 60% occupied when I'm browsing the internet with several tabs. And, somewhat like 80% when I'm playing music, browsing the web and updating the OS.
But, one thing is still there. I don't know whether I've installed the correct driver of my graphics card or not. This is what my current state is:
https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn1/15991_10200384718254047_610397287_n.jpg