As an owner of a virtually identical PC (now fried), I wouldn't bet on it. Maybe low settings would run nicely, perhaps up to medium - but the card is just so far outmoded now. Stunningly powerful, yes - for its time - but incapable of supporting half the modern graphical techniques introduced since its design, and crippled by the other half

And your RAM is probably an even bigger issue. Add more! ADD MORE RAM! Costs very little! =>
Damn, I don't want spend a lot of money on a new computer. If I want improve the ram I must change the motherboard, GPU, CPU and install Windows 7.
For me, in a videogame, the graphic isn't the most important thing and if my PC can run Dishonored with medium setting, for me it's ok.
I hoped that my computer can run all games of this generation... If I can't play at The Witcher 2: Assassins Of Kings, The Elder Scrolls V: Skyrim, Mass Effect 3, Bioshock Infinite and Dishonored with medium setting I'm going to change the hardware of my PC.
I wait the official requirements for PC.