My problem is possibly related to this one since I too have a Nvidia card: http://www.gog.com/en/forum/the_witcher/shouldnt_i_be_able_to_run_this_game_well

Anyway, this is my laptop:

Intel® Pentium® Dual Core Prozessor T4500 (2 x 2.30 GHz, 800 Mhz FSB, 1 MB L2-Cache)
2048 MB DDR3 Speicher
512 MB NVIDIA Geforce G 105M
and I installed Windows XP Professional 32-bit

I'm aware that this is no gaming laptop, but it actually meets the recommended system specifications for The Witcher and the game runs smoothly most of the time even when graphics are set to high. But sometimes during ingame cutscenes it is extremely choppy even on low settings. For example, the intro:
When the narrator mentions time and date and the lightning strikes, it turns choppy.
Geralt runs away - it works fine.
The carriage starts moving - choppy.
Then it works fine until they reach Cear Morhen ... and so on
...most of this happens even on low settings. And, at least to me, there seems to be no pattern behind it. Shure, I guess it is more demanding to display lightning or a vast scenery but the part when they walk over the drawbridge or when Geralt speaks with Triss are choppy too.

I deactivated all power saving features (that I'm aware of), namely the "PowerMizer" function of my Nvidia card (which should not be active when my laptop is on the power cable anyway) and the APM of my hard drive. I recently installed the latest driver for my video card, but this did not help.

The problem is only the fact your pc is not good for gaming, thats all.
You can still play a lot of good old games without any issue, but your video card and processor are not enough for recent games.

Your pc specifications meet the minimum required, that means you can play the game but ofc you cant expect to have good performances.
Consider that laptops are slower then desktops with same system specs, and the minumum/recomanded system specs tag for any game means a desktop with dedicated video card ram, atm im not sure if the 512mb ram of your pc video card are shared or not, but anyway its not the only point.

Tbh as ive played and finished this game, i warn you that expecially near the end there will be situations quite crowded and i had some fps drops with a desktop pc a lot faster then yours, so be prepared.

As you can imagine, to improve a little performances keep your pc clean.
I can suggest to uninstall all you dont need, install a software called "temp file cleaner", its free and its very useful to delete a lot of unwanted junk.
Install a software called JKdefrag, its free and its a lot better(and faster) then windows standard defrag.
This can maybe help a little, but keep in mind that to play "recent" games you defo need something faster, expecially the video card.

Choppy cutscenes are a common issue, which is mentioned in the "Fixes To Common Problems" sticky thread:

http://www.gog.com/en/forum/the_witcher/fixes_to_common_problems/post1

In short, you need to toggle the "Depth of Field" setting in the graphics options. Some players find that turning it off fixes the problem, others find that turning it on does (turning it on fixed it for me). This problem affects cutscenes only as these are the only places where Depth of Field is used.