i'm not sure if I understand you correctly (and the link don't work).
You want to hook your monitors up to your laptop? But you must mean line out into the monitors, right?
If it is a headphone like plug out from the laptop, a stereo out in a single jack, then you need a stereo plug that goes out to 2 mono, left and right.
If you use a mono plug to 2 other mono plugs, then you will, as you noticed, get the same signal at both left and right.
You need something called an "insert cable".
Like this (but I guess your laptop has a small plug?).