how to re-size video all format with the same quality?

The quality of a video file depends mostly on its bit-rate. You will need a converter and

 before converting, set the resolution to 1024x600, set the bit-rate to 2000kbps or above 

(since your original video is 100MB, i guest it's bit-rate is about 2000kbps) Then the quality

 should be as good as the original.

For the converter, get AVS Video/Audio Converter. Just get the trial and try it for 30 days

AVS is the best Video Converter according to Top-Ten-Review research.

In case you need, this is a step-by-step tutorial about converting video/audio.

Hope these help.

Good Luck