Tom, if you've got a couple of film grain textures I could have a shot at making a film grain effect. I'm useless with art though. I guess you'd need a bunch of black-and-white textures that have just the film grain pattern on them, then I could use that with an effect to process the background, and switch randomly between the textures to give the effect of frames going by.
Funny thing is I completed 'Ico' a couple of days ago and figured out today that once you play through it, you get a couple of post processing effects to play around with.
I think the old film / grain effect works through a couple of layers. You have the grain itself, which just animates randomly (David had something like this set through a simple event in an older cap). Then, you have a couple of burns and stuff - means: black blotches and burnmarks that you barely notice, cause the film runs at 24fps. You do see them, but they're quickly gone again. And then you also see a few light stripes 'walking' from left to right sometimes. I have no idea how they're generated, but my wild guess is that that's just light shining through the roll of film. And then the film also sometimes loses its sharpness - I guess that's because the filmroll is probably moving around slightly while being played - but that's a wild guess again.
Also, there's vignetting, which means that the sides of the screen gradually become darker and darker.
Valve has put up a bit of info on what they did for Left 4 Dead on their blog:
I'll try to come up with a Photoshop composition that has those layers in one simple .psd, so you could play around with it. Another thing that'd certainly help to get this old'ish look would be if we could affect the opacity of a sprite through the sine behavior - So we could let things flicker and fade in / out, etc. randomly.
Also, have you looked at the fx file they provided on that site? Maybe that effects looks cool enough already?