It *used* to run fine on 256 MB of RAM with a pretty low-end computer.
Since like 2.6 or so, antialiasing has been added, and that pretty much lowered the fps a lot. Try creating a shortcut to toribash.exe, right-clicking then going to Properties, and adding -aa 0 to the end of the line. I think that's how it was.
Also, what is your graphics card?
And like cayal said, don't run anything in the background, to see if it works. Stuff like torrent clients, file-sharing, etc.