Why does the steam versiion not support 64 bit widows?

Originally Posted by Nike-it

The game supports 64-bit systems, the problems with these systems were caused by the drivers if not mistaken.

What drivers would those be?

Valve seems to think the game does not work well enough in 64 bit for them to support it.

I notice also that my GTX 260 is on a list of unsupported cards. It's a long list including many popular cards.

What is going on here?