Use OJOsoft Total Video Converter version 2.5.1. It can convert whatever you want such as AVI, MP4, 3GP, MPEG, VOB, MOV, WMV, FLV, TS, ASF, MKV, SWF, and Audio.
In addition, you can choose the different device and quality.
It is a very good software. I use it to convert movies and YouTube flv to WMV for my iPAQ 210.
Note: the lower version is not good as this one.