The reason I asked about your free disk space, was because I answered a similar query some time back, where Dvd2one finished before processing the whole task.
It turned out to be lack of Hard disk space that caused the guy's problem.
Bear in mind that a ripped DVD can take up to 7-8gb, then the space required by Dvd2one is 4.36gb. Then there are overheads in XP (Virtual memory etc.) so it's possible that 12 gb is not quite enough.
It might be worth trying to archive some stuff off, to free up another gb or so and see if that helps.