Sorry for empty post, I thought I was just logging in!
I suggest you call iTunes support (if they have any) I'm not sure as I've almost never used iTunes, even for my wifes and brother's ipods (there are better and free alternatives unless you want to buy stuff from iTunes).
As far as I know iTunes and songs you buy from them and iPods get into a weird wedding like relationship. e.g you can not use one iTunes with as many iPods as you like, or you can not connect your iPod to as many computers as you wish. In a similar way, most probably, you may not be able to move your songs to other computers as many times as you wish. Even if you keep most parts of the old computer, a new installation will be treated like a new computer by iTunes, then there'll show up limitations.
I maybe totally wrong, as I have always stayed away from iTunes (because of marriages between devices and some more), but I am quite sure that you must be careful with DRMed stuff when moving them around.
Once I reinstalled my win2k, and then noticed that I've encrypted some files in the previous installation (on the exact same hardware). Only thing that had changed was reinstalled win2k in the c: partition, encrypted files were on another partition, or maybe even hard drive.
Since then, I could not even delete those files (with full admin privilages), let alone reading or copying them.
THG forums may not be the best place, go check iTunes related forums as well. There must have been many in your boots.