Well, that depends on how much money you are willing/able to spend, and on the range of possible upgrades your system (specifically your mainboard) is actually compatible with.

To answer your question: CPU and RAM, probably. For instance, an additional 2GB of RAM can never hurt.

ME2 is a corridor bases fps/rpg with mostly simple environments (that look nice though). The Witcher 2 has a much more open world and way better and complexer graphics.
Increased system requirements is one of the disadvantages of pc-gaming for some, but at least the Witcher 2 pushes the envelope a bit more. We're already stuck with more or less the same graphical quality for more than 4 years.

But I understand that you don't like it, because in the above posts it becomes clear that upgrading your pc will be expensive. Some RAM and a new GPU is a good start, but in the long run you should look to replace the Motherboard as well, so you can have a decent CPU upgrade, but that would also mean other ram in some cases.....
So think about what you want, is it worth upgrading now to get some moderate performing pc that will be outdated in a year, or is a complete overhaul a better idea?

You're right i'm better off just buying a new pc. But saving that amount of money will take a while, cause i'm 17 and still in school. I'll just stick to xbox360 for now with newer games.