Could you supply more details, such as if this is for PS2, and a link to the filemanager.
I personally use ulaunchelf for all my file managing on the PS2. I also use HDLoader and Open PS2 Loader in that order. Other than that, I have a PC so I don't use it for movies etc.
I do know that the ps2 Internal Hard Disk uses it's own format. You have to extract the games into ISO's either accost a network or directly to a computer via IDE link cable and manually move the files to a USB drive. As for external, I'm not too sure since the PS2 uses USB 1.1 which is abysmally slow and I have an internal HD so why bother?
Now if this is for PS3, I won't know till tomorrow (or a week from now) since I'm possibly going to get a PS3 based on their invoice listings in the inventory.