Dude, I'm seconding in. I've wanted to know how people do this whole TV-to-computer transition, too for my own little projects. So...*placing hand on shoulder*... you have my cluelessness, Craig.

*Laughs*

If it helps, I've done enough research to know that a device called a USB Capture Card exists, which is a hub that lets you attach RGB into it and then connect to the PC.

What would be ideal is if I could do that while the signal was still going to the TV, though *furrows brow*

Since usland doesn't use scart, i assume by RGB you mean the red, white and yellow cable from the wii/gc?

Then all you'll really need is something like a phono splitter. So you can split the signal to go both into the TV and into the usb capture device from the single source (being the wii).
http://www.maplin.co.uk/Module.aspx?ModuleNo=9662 <- Something from your usian equivalent like this should do the trick (and don't worry too much about the colours as long as you follow the cable through to the right place). Also remember that usland videos will be ntsc 60Hz and if uploading to youtubes to make the vids as 10 mins or less at a time.
I might try to knock up a diagram if the phono-splitter idea makes little sense.

Thanks Creo. I'll look into it from here. Can't say how long it'll be before purchases, but I'll reply back when results are achieved.

you have my cluelessness, Craig.

AND MY AXE

goddammit turtle i was going to say that