Don't think you can control the name, the first USB device plugged in gets named 000, the 2nd 001 etc.. You can work out if it's your ext. HDD by going into the directory though so it's not too hard.
I just copied some ROMS over to the program directory on my internal HDD and they run from there also. Considering it's the first release the playability is excellent.
Will it ever be in higher resolution though? 480p isn't the best.
Doesn't seem strictly true regarding naming, everytime i plug my usb device in its dev_003 and its the only one plugged in, i had to resort to using the ps3 ftp program to rename it!