Cant convert videos

so, i’ve downloaded a couple videos online, and they are using xvid codecs… now, my windows media player plays them fine, but when i try to bring them into Premiere 1.5 or After Effects 6.5 to convert them, they dont play… but heres the wierd part… in premiere the little preview in the imported media window will play, but if i place it in the actually timeline, it only shows up black with no sound… same type of thing in after effects, except something about cant find first frame appears in that… now ive tried using other “video converters” (imtoo, No1, etc), and they seem to work, but dont give me the right output settings that i want… does anyone know why these videos wont work in these adobe programs?? thanks in advance!

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