Which program should i use to edit a flv. video?

Its because i need to edit 3 realplayer videos. I used Windows Movie Maker and I import a realplayer video but it said something about the format. I need help.

Try out VLC media player. You can play and convert almost any video format with it.
http://www.videolan.org/vlc/
It's free and it's open source.
It takes a little work and some fiddling around, but I have converted FLV to WMV with it. Then you can use Movie maker to do whatever you want with the file.