I believe most editing programs won't like editing with .rm or .ram (Real Media) files. The general recommendation is to use DVDs as your source footage if at all possible. For all other video sources, you should convert them to something that the editing programs can deal with better, like Huffyuv or Lagarith lossless compressed AVIs or Uncompressed AVIs if you have the hard drive space. Avoid editing directly with DivX/XviD/other MPEG-4, Real Media, Theora/VP3, Flash/VP6, and other lossy codecs.
Having trouble playing back videos? I recommend: