I'm Trying to Download a Slider on ModtheSims

Hi, I'm trying to download a butt slides from modthesims.info. I really want this, because I know it'll help me! But, I recently got a Windows 8 laptop, that can't open .packages! And all the sliders are .package format. It opens .sims3pack's, but I can't find a butt slider in that format.

Does anyone know a way to convert it to a .sims3pack or does anyone know where I can get a butt slider in that format?

Thanks! My laptop type: HP Windows 8 Laptop