The name of the libmtp-hal package is probably standard. If your distro uses HAL & udev, it probably has it.
The name of the fdi file may be different than 10-usb-music-players-libmtp.fdi. You also need to insert the segment in the correct place so you don't end up with an invalid xml file. (If that is your course of action) Of course, make a backup of your old file, and examine it first to make sure it makes sense. My system has a usb-music-players fdi file in /usr/share/hal/fdi/information/10freedesktop/ as well. The YP-U3 isn't listed but other sansa devices are. The one in 20thirdparty is probably an update with newer devices, which haven't been added to the freedesktop.org standard fdi files yet.
Yes, if your system has it's own version containing the fdi files, use that instead of inserting the segment I posted. Also make sure that the dbusd and hald daemons are running. If you boot with the noacpi option, they won't start.
Also try the sansa site and see if they have posted fdi entries to add or a .fdi file.
You might try monitoring /var/log/messages while plugging in the device. Sometimes there is valuable information logged.
Last edited by jschiwal; 03-15-2009 at 02:05 PM.