There's a big 3GB archive in the Downloads section that I'm pretty sure contains one or two versions of the TWL SDK.
I can't leak it myself, due to the NDA still being in tact. There is no Software for Linux from Nintendo (Windows only), plus the TWL stuff didn't get Updated in a long, long while, so chances are high, that the SDK the guy/gal above me tells you about is up-to-date (I didn't check it out myself).
It's SDK 5.5 (12-07-2010) and System 2.2 (18-09-2009), right now. There aren't much differences between 5.5 and 5.4, anyway.
I assume you cant do actual development with these? Are these only meant for testing? If so, what do you do development on? As in the binarys.
The IS-TWL-CAPTURE does have a Nintendo Wii AV connector. Does anyone know if it outpouts Component Video (YUV)?
It does not output component. Composite and S-Video only (and that only if you have the video-out option installed). Also worth noting that the SD and flash cart ports on the debugger will not work for making backups of retail games. It only works with flash carts. You may be able to read the save data from a retail game -- I forget. I no longer have my Debugger. You can't even write dumps of retail games to a flash cart. You have to have a .SRL (master) image. Some of the protos floating around the net are also writable to flash cart.