Converting to AVI another codec, then messing up sound!

Hi, i'm a newbie and i'm needing some help to convert AVI - VCD... - I kind of got the basic, but some AVI files, is messing up sounds (picture slowlier than audio) - and that's is a real big problem for me!, because when i'm converting to another codec which is required for TMPGEnc (only can take a few codecs) There are also some unreadable frames as VirtualDub calls them! - how do I remove them, because I think it's the first thing you got to do, because you can't convert them in VirtualDub, either. - What shall I do?? - I need help, please!