Avi files play but mpeg copy won,t

avi files will play perfectly on media player but won,t when i convert to mpeg2 files. cd check on mpeg files report no problems, but couldn,t check avi files as it says no suitable codecs installed. g.spot on mpeg files when rendered says video mpeg 1 stream splitter mpeg video decoder, audio mpeg1 stream splitter ffdshow audio decoder, all i get when playing mpeg converted files are odd coloured squares on media player and stand alone player, all very confusing, can anyone explain

An working mpeg2 codec is necessary in any case!

mpeg1 is not mpeg2.