There are tons of converters out there, but since you could not find them on your own, you probably want to use the simplest one, www.slysoft.com, they have software to convert to mobile standards.
Once you have your movies converted, I recommend using doubletwist to manage your music and movies. It makes transferring media to your android device very easy.
You just copy and paste them in the folder you want. 3.1 should support many formats, as my 2.2 on galaxy S does, and i copy video clips or movies, xvid, h264 and never had a problem until now.