Converting flv to avi without generating HUGE file size

[Kat]

I regularly download streams and most of the time with success. The problem is the conversion. I do it and the resulting video quality is more than adequate but I wind up with HUGE file sizes.

I'm currently using iWisoft which is free and has other functions which I like. As an example, yesterday evening I download a stream which was 100 MB in size (640 x 480) pixels. When I go to convert it, it winds up being 235 MB. I don't really want to skimp on video quality. I know someone who records the exact same file as me and yet they have avi files that are ~ 100 MB, the same as the original, the quality seems to be on par with the original too. I asked them what they did, no response.

Is it a magic codec that I'm missing or should I just use something else?