Migrate from Server 2003 to Server 2008 Test - then live

I have seen several comparable questions, but I wanted to see what worked for someone doing a phased approach to this.  I have an old file server running Server 2003 standard - I need to move about 250gb of shared data from that server to a new Server 2008 Standard R2 box.  I would like to move it with all permissions (shares aren't a big issue as I only have 5 total), however, I want to do a full move on a weekend & then do updates over the course of a few days until I am able to do the switchover.  Has anyone built a robocopy command or something similar to copy all files, including permissions and then be able to re-run it to update the changes since the last time?

I want to get it 100% setup & get the new backup working well BEFORE I roll forward with deploying it.

Thanks!