How do I copy video files (avi and other formats) to my Nokia E90 phone?? How do i convert them to mp4 so that they are optimized to be played on my phone??

You may try Aimersoft Video Converter, it can convert all types of video including AVI, WMV, MPEG, FLV, etc to MP4 for your cell phone, my friends recommend it to me, very easy to use and works perfect for me, here is the official site
http://www.aimersoft.com/video-converter.html
If my answer didn't solve your question, you can use yahoo!answer to search for more answers or email me
http://answers.yahoo.com
hope it helps.

I recommend using Smartmovie as it can convert the video for the inner widescreen. You can download it here