Sometime ago it was available. Not anymore?
I finished TW1, and was going to uninstall it, than remembered that I could get the game all patched-up from GOG, redeeming the game from the serial of the physical media, in event I would like to install again for some reason, it would be easier to install. But tried and it doesn't worked.
It was only temporarily available?

Have you tried this link?
http://www.gog.com/witcher2/backup

I've redeemed a Steam code for Witcher 1 around two months ago, and it worked without problem. Make sure you wrote the code correctly.

And alternatively go here:
http://www.thewitcher.com/backup/

Thanks, I didn't found this link before, I was trying from the generic redeem link. Now it worked.