I've heard that filming in 24p on a digital camera can help you achieve a "film" type of effect. Is this true? Are there any advantages when shooting in 24p? Or is it safer to keep it at like 25p - 30p?

yeah filming it on 24p can help with the film look, just make sure your editing software has support for 24p

i have adobe premiere cs4 but i havent used it yet, does it support 24p?

I have cs3 and it supports dv 24p so Cs4 should have it

I've also heard of software that can down convert 25p to 24p. Would this be any good? In case I filmed in 24p and it looked terrible?

Actual film cameras run at 24 FRAMES PER SECOND. It helps with the motion effects and the blurring of the video cameras to achieve the same frame rate, but it isn't a magic button that makes a video look like film.

Some cameras, like the Panasonic DVX100 and HVX200, as well as some other cameras have some kind of "cinegamma" or "cinema color" which is the color settings that give a more "film look" style to the footage in the camera. Even this is NOT a magical switch that instantly makes footage look good or compensates for bad framing, blow outs, or massive contrast changes or poor focus.

Adobe CS1-4 all have support for some types of 24P, including standard definition and high definition.

Shooting at 25 Frames Per Second is tricky because if you shoot in the INTERLACED format which is really 50i (or 50 interlaced fields per second), that is what is most commonly seen as the "video look". You can make it progressive and slow it down to 24 Frames Per Second, but it will not be the same thing as shooting 24 FPS or even true 25P frames per second (progressive).

As Sonny said Frame rate is one pieve of the puzzle. You need to concentrate on DOF, Lighting, etc.. . as well.

Here's a free tutorial on making 24P from various frame rates...

http://www.videocopilot.net/tutorials/frame_rate_converter/