Try Machete Lite.
It works only on AVI and WMV files, but is a lossless editor--you suffer no degradation in quality when you edit.
It's a free download. There is also a regular (non-Lite) version that costs money and has more features, but for simple editing out segments as you describe, you don't need anything but the Lite version.
It's quick, simple, and works very well.