Okay, so I managed to get a very basic Oscilloscope function running on the screen from software. By using a buffer I'm able to get adjustable response speeds.
The way I have it hooked up is to have the input read from analog port 0 and 1. on port 0 is the sensor output and on port 1 is a capacitor used to adjust the size of the buffer.
The limiting factor at the moment is the TVout library, which is very slow on the arduino and has a maximum resolution of 128 pixels wide (the library says 160 but I can't get that to work...)
I don't know what frequency this thing is capable of working it...but to hazard a guess I'd say very low, somewhere around 60Hz with a buffer size of 1 and around 1920Hz with a buffer size of 32.
So, in short, to arduino software approach isn't really viable.
Here's pic of it in operation:
and a short video. It's just hooked up to an LDR at the moment because that's the only thing I had laying around!
Here's the link: Homemade Oscilloscope Operation - YouTube
This is as far as I'm willing to go with this, after hearing lots of people talk about it online it just seems too complicated. However, it is nice that I got some working functionality from it, even if it was limited.