I noticed a Knowledge Base article that addressed the firewalll issues some have experienced:
http://docs.info.apple.com/article.html/?artnum=93434
Also, the article below has an explanation of some of the error messages in iTunes for Windows and for OS X:
http://docs.info.apple.com/article.html/?artnum=93431
[This message has been edited by swise (edited 11-04-2003).]