Hmmm... interesting question. What "vintage" are you looking for, exactly? There are a few, probably interrelated, questions here:

1. Is it a particular time period?
2. Is it a particular look?
3. Is it a particular photographer?

Sometimes, as Chris mentioned, what makes the photos look the way they do is a combination of technical factors inherent in the equipment itself. Sometimes it's in the subject matter. Take portraiture for an example; not only has the appearance of the photo itself has changed, but types of dress change over time, and the poses used in portraiture of even a relatively recent vintage -- the fifties, for instance -- is different than today, and also different than what preceded it from, say, the 1890's. Photographers working in the same genre have also relied on different forms and techniques over time. Matthew Brady, Robert Capa, and Nick Ut may all have been war photographers, but their approaches to their subject couldn't have been more different.

So what's this mean for you? In short, it comes down to two things: figuring out what you're trying to get across (what's this picture about, and how integral is the vintage appearance to that?); then, paying attention to details. The wrong detail (a vintage diner with a Scion parked out front, someone in Victorian garb doing the Macarena) can wreck the effect even if you've gotten many of the other bits right.

I completely second chis's post, however I'm not sure if that's what the OP is actually going for. I think a little bit might be getting lost in the vernacular. Maybe I'm wrong (and if so enthdegree, please correct me!!) but it sounds like enthdegree is more looking for that processed "vintage" look, you know the difference between that vintage look and that "vintage" look. If that is the case, just download some lightroom presets and go that route.

'vintage' effects are the result of a couple of factors:

a) decreased contrast from use of either single coated, or uncoated optics)
b) smoother tonality stemming from use of larger film formats (120, 4x5, 8x10, etc.)
c) different approaches to lighting than are popular today

if you want vintage, get yourself an old twin lens reflex camera on the cheap (ie. a yashica-mat, minolta autocord, or rolleicord), and use that. These cameras tend to use either tessars or tessar copies, some use three element trioplans or triotars, for their taking lenses which will give a far different look than the overcorrected multicoated zooms of today.

also, study the work of contemporary photographers from the 40's, 50's, and 60's, looking at their approaches to light will have far more influence on the 'vintageness' of a photograph than the equipment used.

Why not use a vintage camera ? It would be the easiest in my opinion. You can find very cheap ones on flea markets. Of course, that means going back to film and lab processing, but it's good to do that from time to time.

Hello, everybody (^:

I was wondering how I could go to make my lenses take more 'vintage' looking photos. I know I can achieve this effect to a certain extent by playing with curves and simulating soft focus during post-processing but it always comes out looking very hard and unnatural.

I was thinking maybe using a soft-focus filter over a sepia or reddish filter on my lens. (Or instead of the soft-focus filter I could just get another uv filter and smear vaseline all over it like others have mentioned here. That might be hard to keep lint and hair off of though.) although stacking filters might degrade image quality a bit too much.