I have an ESATA port on my laptop and I flashed my 360 with an ESATA to SATA cable BUT I had to follow steps listed here
http://forums.xbox-scene.com/index.php?showtopic=701119 to switch to IDE mode in my BIOS. Without that it wouldnt recognize my dvd drive and is apparently the case for most laptop users (hence why some people think you can't use an ESATA port) but if you use that guys registry files (link lower in the thread) then it works!