Icon packages - IP and PNG

Hi, everyone. I'm a newbie here, so if I'm violating any rules, please let me know.   

I'm actually using RocketDock instead of StarDock, but I've learned that I can use icon packages from several dock programs. However, I've come across a problem.

I tried downloading a few packs from here, which are all .ip files. Turns out I can't open those, my computer doesn't recognize this kind of file. Can anyone tell me what program I need or what else I have to do in order to be able to open and use these files? I would be eternally grateful.

Thanks heaps!!