This particular panel has a digital (SPI) interface, which means that you'd need to digitize the composite video signal, down-sample and format the pixels before sending them to the panel. If you need 8 bits per pixel, you'd have to sustain an effective throughput of 614.4 kB/s for full-speed video (30 fps).
You'll be better off looking for a panel that accepts composite video directly. The controller for such a panel has these functions built into it.
If you really want to try to do this with this display, I would recommend getting something like the BF561 EZKIT from Analog Devices. This board includes a chip that can digitize the composite video for you and convert it into RGB data. It also includes a powerful DSP chip (the dual-core ADSP-BF561 "Blackfin" processor) that has more than enough horsepower to scale the image down from NTSC resolution to the 160×128 that the panel needs. It also has a high-speed SPI controller that can communicate with the panel. The only hardware development you'd need to do is to get the two boards correctly wired to each other.
On the software side, you need to accomplish two basic tasks: get the video scaled correctly and then pump the data out to the panel through the SPI interface. ADI has lots of code examples for both of these tasks that will help get you started.