there are many ways to trabsfer movie files to your unit you could install TinySMB from AppMan or try what i do i hope this can help you

in your windows pc:
download the Java Mini Web Server
http://www.jibble.org/miniwebserver/

save it on some folder
c:\somefolder

then goto cmd (click on Start -> Run -> type cmd then enter)
cd to c:\somefolder

from there execute the jar file
type: java -jar simplewebserver.jar

on your n900
click on browser then point to the ip of your windows pc


or the easiest way is you could just plug in your n900 to pc as storage device then copy over the files