Premiere Pro yello line on import

hello,

whenever i import a video file into premiere pro cs5.5 i get a yellow line above the clip in the timeline and a need to render the clip before i can get smooth playback.
i also fear that the rendering is creating a copy of the video file on my hard drive and taking up almost twice the disc space (now having 2 files).

i have downloaded neoscene and tried trans coding the file first. but the .avi file neoscene gives me still comes in yellow.

my question:
what is the native file type (or what trans coding do i need to do) to get an imported file to come in 'green' on the timeline in premiere pro cs5.5?

detailed descriptions may be necessary as i am a noob.

thank you in advance for your help.

Ben Oakley