Downloaded ifp manager
(archLinux tutorial, check for other operating systems in search engines). Also downloaded usbview. It tells me that my USB is in /proc/usb/devices and can perfectly be found. Okay, so I run:
# ifp ls
iRiver iFP device not found.
Note: Please check USB connection.
Checked everything and still could not solve that.
Then, browsing in one forum, found the message, dated to December, 2005:
I have the same problem as mentioned earlier about the iRiver T30 on ubuntu. After reading through some threads on the misticriver-forum, I found out that the US and European version can't be used on linux because it's firmware is based on mtp (microsoft "secure" firmware) which ties it as mentioned in an earlier post, to windows media player. Further more iRiver isn't planning to release any ums-firm/software for the t-models, so all in all it seems that we just have to wait and see what iRiver does or someone manages to find a workaround.
Okay then, so I am short of ideas. Damn...