VirtualDub is fantastic for anything in an AVI container (DivX/ Xvid). I highly recommend it, since you can both do simple editing (as you requested), and re-encoding to lagarith which might be necessary in some situations.
WMV might be trickier. I've never tried editing it. You'll probably have to use AviSynth and VirtualDub together to do the cutting, and re-encode the result
Also, keep in mind that (without re-encoding) you can't simply cut on any frame you want - you can only cut on "intraframes" (or keyframes), which in the best case happen every ~10-20 frames, but in the worst case can happen every 240 frames or so. Usually there will be a keyframe somewhere in a scene change (i.e. at the start or end of commercials), but not always
"Smart re-encoding" can get around this, but most software doesn't support it, and most that do only support it for MPEG-2.
Lagarith and other lossless codecs are "intra only" which means every frame is a keyframe, simplifying the editing process - hence my recommendation.
~MiSfit