Both Witcher games are free to play (don't get that phrase confused) on Steam this weekend.
If you like them, they're dirt-cheap to buy as well: £2.99 for The Witcher 2, and £1.39 for The Witcher 1. Offer ends 18th February.
What a disgusting discount.
To play for free, head to the game's Steam page, scroll down and click the big "Free Weekend" button. Steam should do the rest.