If the origianl file looks ok, you probably don't have a problem.
First check to see if your audio matches the project settings....if you audio is 48 kHz, than you'll want to make sure your project settings are 48kHz instead of 44.1 kHz.
Also, it is best to use a video format that is native to the NLE....If you are using premiere on a PC than the ideal format would be an AVI using the built in Microsoft DV codec. (this is typically automatic, but there are some exceptions)
If the format of your video is not native, it will not play smoothly until you render it. If you render it than add an effect, you'll have to render it again to play properly.
Another possibility is that your computer may just not be that powerful.
I could be more specific if I had the following info:
-Operating system?
-Software (NLE)?
-current format of video?
-how did you get the video from your camera to the computer?