Help editing :(

[chez:O)]

Hi how can you edit a clip which was downloaded off the net with windows media/i-movies/pinnacle. i just want to edit it and add music so i can put it on the net. Could anyone help cos when i try and load the clip to windows media but it doesnt recogise it, whys this? Have i got to do something to the clip using software first? If so where can i purchase the software?

Can anyone please help me :)