I would suspect the HDD is at fault here. SMART verification isn't always that reliable. Get out your restore media and run Apple Hardware Test (the extended version). I'm betting your HDD will be flagged as failing. HDD failures in laptops is probably the single most common hardware problem people have. It's a small wonder you made it to 3 years. You must really baby your laptop.
And I must say, you have far better english than quite a few native speakers. If you hadn't said something, I probably never would have even thought it's a second language. You are to be commended IMO, since english is a language of exceptions rather than rules. You have a grasp of the word "the" and you know the difference between to/too/two, contractions, even some colloquialisms such as the way we have a penchant for overusing the word like and "crappy". Usually people in Europe are taught British style english, which has some subtle differences. I wish I could speak a second language with even half your demonstrated skill. Seriously.
Give Apple Hardware Test a whirl and let us know what it turns up. One of the two restore discs that came with your system will say something about running Apple Hardware Test right on it. I assume you can do the translation given your obvious command of english. You must be near impeccable in your native tongue.
I have a macbook pro, 2.4 ghz, 2 gb ram, graphics nvidia geforce 8600 - it's about 3 years old.
The problem is that my mac is becoming slower and slower, sometimes it becomes unresponsive with simple tasks such as loading several tabs in the browser (i normally use firefox). And it happens too with photoshop, illustrator and basically any software.
The worst, is running 3D software in it. Some few months ago i could work fluently on a 3D project, now i just can't make anything that it just breaks down or crashes. Even scrolling windows is a pain in the b*tt.
I know that 3D software might be way too heavy for a 2gb ram and my graphics ain't the best... but i'm sure something is wrong with my computer because it was working fine some months ago...
I've been making software updates, i use Onyx like once a week to run the scripts, i've made a SMART hardware checkup and it says it's everything ok...
The harddrive is 160 gb and it has 20gb free space. It doesn't have much space left, but i don't think this could be the source of the problem.
Could it be a graphics card problem? i've been looking for drivers update in nvidia website, i can't find them for mac.
Or maybe some more extra ram could resolve the problem. But i don't know if i want to take the risk of spending 200 euros on + 4gb for nothing....
i'm clueless, any tips/help is greatly appreciated!
PS - Sorry for my crappy english, it's not my native language