This is the kind of situation where a 64 bit system is precious. I tried it now on my Vista64 and it renders a infinite water plane with your specs, at 3200x2400, in about 20 minutes. The memory count reaches 1.3GB.

During this process, I found that the water doesn't look very realistic on close-ups... I can't put the entire image here, it's too big, but zoom in on this part I attached. Weird.