I just spent a couple of hours fixing this problem, so now I can share. I just bougth a 3TB WD external hard drive to ad to my BoxeeBox but the machine just wont recongnise it. I think it will be the same with the Xbox or the PS3. Here is how I fixed the problem. First, the drive must stay in MBR, if you change it to GDT, it wont be recognize.
But in windows, you cant do any partition of more than 2TB, so will will have to use a third party program. The one that I used is Acronis True image (WD edition) it was free on the WD web site but you can only install it if you have a WD product already installed. You can have the same Acronis under other names by other brand name web site (Seagate diskwizard…). Just be sure that the program have the extended capacity manager option. You should see it in the userguide of the program.
First, be sure that all volumes are erased on the new hard drive by going to: control panel, administrative tool, computer management, storage, disk management. Then right click on the volume on your disk and click erase volume.
Second, intall the Acronis program. In the Acronis program, go to disk management. Then add new disk. Click on the empty disk. Then on the left row, initialization option (chose to create an MBR disk), in the left row, chose partition, then by clicking the volume available, you will create 2 partitions. Each must be less then 2TB, click Proceed.
Hope it helped.
Enjoy.