Can't copy music to ipod ("cannot be updated... unknown error (-50)"

Question

Well, the last month has been pretty much a nightmare with my beloved ipod (60gb with video, and I'm using a Powerbook G4).
My immediate problem is this: after transferring about half of my music onto my ipod (which I'm doing from scratch, because of another issue that will come up later in the post), I got an error message saying "The ipod 'Disco Stu II' cannot be updated. An unknown error occurred (-50)." I click ok, and am stuck here. I cannot eject my ipod - when I try to, I am told that "it contains files that are in use by another application" - although I'm not running any other programs (except, currently, Firefox). When I click "ok" to that, the first error message recurs. When I close itunes and move the ipod icon from my desktop to the trash, I get a message saying that the disk is in use and could not be ejected. Relaunching Finder doesn't change this. Reopening itunes, nothing changes. It's possible that if I restart the computer, I'll be able to eject the ipod, but this also seems like it might end up doing more damage.
The larger problem: this type of thing has been happening often recently. A few weeks ago, I was copying music from an external hard drive onto my ipod, when itunes suddenly quit. I don't remember all of the details, but I got a message saying the ipod couldn't be read or written to. I said ok, ejected the ipod, and to my horror found that it was now empty. When I plugged it back in, itunes gave me a single option to restore the ipod. I called AppleCare, who walked me through an alternate version of restoring (unfortunately, I don't remember the details here either). I was then able to put music back on my ipod, and for a few weeks it worked okay. But last night I had my ipod plugged into my laptop's usb for charging, and while my back was turned another error message (I think this was another "cannot be updated"), and again I was stuck with a single "restore" option, so once again, I had no music on my ipod. Which is why I'm trying to refill it now, without much luck.
Other possibly relevent stuff: earlier tonight, while my ipod wasn't connected, itunes caused a kernel panic. I thought (hoped) that this meant my copy of itunes was the problem, so I trashed my copy (as well as my itunes preferences... but are there other things that I should also be trashing?) and downloaded and installed a new version. Apparently this wasn't the solution, since the immediate problem happened after I installed the new version.
Any help appreciated. This is the kind of thing that makes me want to cry, or throw things.
Adam

Answer 1

Update: I restarted the computer and, surprisingly, itunes could read my ipod and was able to transfer music to it. I still received one or two of the "unknown error" messages while transferring the rest of my music (carefully, less than 100 songs at a time). However, I'm still unable to eject my ipod either through itunes or finder. I was only able to do it by restarting again. Knock on wood, the situation seems tolerable now, but I expect to be living in fear that my ipod will stop working for the next few weeks. Any wisdom would be appreciated. thanks!