Red Giant Psunami is perfect for that. It’s a very high-quality water simulation plug-in that can make photo-realistic water in AE. for underwater scenes use it and then also apply Trapcode shine or CC Light Rays to get the shimmering rays shining down through the water.
I don’t have CS2 but you should be able to just place the shape layer below the layer you want to clip and Alt+click (or right-click) between the two layers in the layer panel to create a clipping mask out of the shape layer.
I think it should do that automatically since the GT 120 is not an approved card so AE should ignore it and use the approved quadro card. To verify which card it’s using go to the preferences>previews>gpu information and be sure “ray-tracing” is set to “gpu” not “cpu” and it will show the card info.
Mattrunks has a tutorial on something similar done using trapcode form 2 if you have that plug-in. The tutorial is a not free but it only costs about five bucks.