Help with removing tedious GPU heatsink! (8800GT)

Hey, I've been trying to get the heatsink off of this graphics card (so I can replace it) but the clip thing used to hold it in is one i've not seen before, and my efforts to remove it seem fruitless, here's the clip;
http://img502.imageshack.us/img502 [...] 001mc2.jpg

It's an Inno3D 8800GT, i've tried everything, spent the past hour looking for possible guides for this sort of clip on google but nothing. I think the four pin-clip things are meant to be pushed down and pulled out, but I can't seem to do it, could anyone enlighten me on what to do please? thanks!