I have windows vista and ati's x1950 pro, is it enough to run just cause 2?
Maybe if you turn all detail down, but it will also depend on your CPU.
Go to http://www.yougamers.com/ and click on the "Games" link and then find the Just Cause 2 game in there to run a test on your system to see if it can handle it. I think you might be disappointed though depending on your CPU. I can say that your GPU is way out of date and will more than likely not be able to handle it.