Ah Wolfer mi amigo, let me lay some knowledge on you son.
Essentially, we believe you're video editing program (Vegas) is having trouble with your source footage format (the file type of your Naruto videos).
So you're gonna need to download and install two things, all free of course. One is a video converting program called Virtual Dub, found here:
http://virtualdub.sourceforge.net/
The other is a series of programs and codecs (video compression methods) combined into a program called "AMVapp", found here:
http://www.animemusicvideos.org/guides/avtech/amvapp.html
Once you've installed both, open virtual dub, and open up a video you need. We're going to convert it to a better format. Go to Video > Compression, and select Huffyub 2.11 (better known as Huffy).
Now just go to file > save as AVI, and save your video into a different folder somewhere. Try importing this video now, if it works, you can convert all your files to this format.
Be AWARE! Huffy takes up lots of space. So make sure you have a lot of free hard drive before you undertake this task.
Let me know if that works for ya
http://www.ashampoo.com/frontend/products/php/product.php?session_langid=2&idstring=0137
Movie Shrink and Burn 2 should be what you need. This one is not a terribly powerful program, but it does a good job. Plus it has a free trial.