ArcticMonkey
Bronze Level Poster
That Optimus looks like a great build although I would upgrade the intel 330 to the 550. it's a fair bit faster and yes you can install your own operating system, my friend did it. The AUO screen is apparently amazing, and if the main reason you want it is media, then you would want it. And as Adli said, the external drive is cheaper, however you'll have to carry it around with you all the time, and some even need a external power supply, so I would recommend getting an internal HDD as your second drive.
Also you can upgrade to blu-ray, it will be within your budget
i'll keep that in mind. cheers lad