For a really large LED wall, you're probably going to need to stream the data over USB from the Raspberry Pi to another board (or multiple boards using USB hubs) that can output the data fast enough for so many LEDs. The USB is designed to efficiently move lots of data... and you're going to need the Pi working on processing the video and converting it to LED bitstreams.
I've written 2 of these applications, which work with 2 types of addressable LEDs Adafruit sells.
If you have the LPD8806 strips, you'll probably want to look at this:viewtopic.php?f=47&t=25854&p=143049#p143049
Here's a project where that code that used it for a video wall:http://www.dorkbotpdx.org/blog/armatron ... video_wall
Buried on that page is a link to the source code on github... the code which reads the video and send out the USB port. I believe they used a small form-factor PC and a USB-based video capture device, so it read the video in, converted the data for LEDs, and streamed it right back out another USB cable to the board driving that LED wall.
If you're using NeoPixel, you'll probably want to use my new OctoWS2811 library:http://www.pjrc.com/teensy/td_libs_OctoWS2811.html