Here's a little project I've been working on. It's a Nintendo DS hooked up to 2 Tablet PC screens, using an FPGA in between to do some translation magic. Pen input from the Tablet PC screens is sent back to the DS. It can also dump screenshots to a PC via serial port.
(Click for big pictures)
Some new pictures. I recently sold it, so I've fixed it up a bit. Wires sticking out the back were replaced with an IDC40 connector in the GBA slot. Touchscreen input was improved to allow both screens to work simultaneously (watch the video to see what I mean). Audio and power were brought out to the connector to minimize cabling mess on the DS.
Another update. I stuck on a USB module (Cypress EZ-USB FX2LP) to allow video recording. I had to write new firmware for the USB controller, as the default firmware provided by Digilent is nowhere near fast enough to transfer video at a reasonable rate. YouTube video shows a PC app I wrote that displays the output and saves to .AVI.
Ooookay ... since this has hit Digg etc., maybe I should fill in more details.
Parts and approximate cost (you can do better scrounging for stuff on eBay):
Grand total: $580 (let's make it an even $600 for any other miscellaneous junk). However, _MOST_ of these things were spare parts I had laying around from earlier projects, so it didn't cost me anywhere near that much. I wouldn't have bothered if it did.
The FPGA takes care of pen reading and scaling up the display. No, it doesn't do any filtering, though that wouldn't be too hard to add. The top screen is capable of reading a pen, but of course the DS only has one touch sensitive screen so it's not used.
More techy stuff, if anyone's feeling ambitious...
The closest match I could find to the DS LCD is Sharp LQ030B7DD01. You can find a datasheet Here. Aside from RGB, the only LCD signals I needed to use were DCLK1 and GSP1 (everything is conveniently labeled on the DS PCB). GSP1 is vsync, analogous to SPS in the datasheet. I find hsync by counting clocks (263 per line). If you need the actual hsync signal from the DS, you'll have to find it yourself; I don't know which one it is. The bottom screen data is latched on rising clock edges, top screen is read on the falling clock. I had to buffer a full frame in ram because screen timings didn't quite match up (incidentally, this also made adding the screen capture ability very easy).
If you're outputting to a large LCD, it most likely uses LVDS (hence the extra LVDS modules I needed). You'll need to find a datasheet for your particular LCD to find out how it's hooked up. You'll also have to figure out how its inverter (i.e. the backlight) is controlled.
If you want to do pen input like I did, you'll have to mimic the DS touch controller. A datasheet for that is Here. The screen I used has a Wacom digitizer. I figured that part out by looking at Linux Wacom driver code (specifically the tablet PC driver; there are different types).