How to make my digital slr photo's grainy?

I need help. I want to get that film photo look without having to use a film camera. I have a nikon d300.Im only 14, so i don't have any money to buy like photoshop, so I'm stuck with iPhoto on my family mac. Is there any way at all to make my photo's look more grainy?

Cut out the middle man. If you want a photo to look like it's been taken with film, then use film. You can't recreate it faithfully on a computer easily.

Head to ebay and buy yourself a 35mm SLR and couple of lenses. They are cheap enough on Ebay these days. I recommend a Canon A1.

Colour negative film is still widely processed and you can even get your pictures scanned and burnt to DVD.

Slide and B&W film needs to be sent to a pro lab, or learn to develop yourself.

BTW, film isn't always that grainy. Look up Fuji Velvia 50 and you'll see what I mean.

Actually you can find a plug-in to emulate many different film types.

Since you are a student, you can buy Photoshop as a student for under $200. NIK and onOne companies make such commercial programs that can be used with Photoshop

For less than about $100, you can always buy a nice used Nikon camera that can use your Nikkor lenses.

Shoot at a high ISO. It will make your images grainy but the grain will be colored so this works best with Black and White images. Iso 1600 and up on most DSLR introduces ALOT of noise to the image.

As Eric says I higher ISO will do it.

Also, you can download GIMP for free which has many of the features of photoshop.