Why do my flip videos lag in wmm?

someone please help me! i make music videos on youtube and i use a flip to film with, well my videos lag really bad when i put them in windows movie maker!!, and for when im vlogging editing isnt a big deal but when im making a music video my triming must be perfect or the whole song is off sync! and when the video is lagging its quiet hard to tell where i am basically. and when i publish it to my pc it works just fine someone please help me i love making videos but i just cant if i cant edit them!