Ugh, now that I think about it, I made a mistake by even using the term "video driver", since someone might mistake that for a codec or something . What I meant was the graphics driver, in my case the ATI Radeon one.

I guess the only valuable lesson here is that it's important to download and install graphics drivers manually, since the "Update Driver Software" in the Device Manager can't always find the latest ones.

Here's a link to a thread about a similar problem:

http://www.gog.com/forum/general/getting_internal_error_when_installing

Edit:
And another link:
http://www.gog.com/forum/the_witcher_2/cant_install_floating_point_error_at_1821