Can you stream songs through other sources like Amazon.com or Rolling Stone.com - I'm wondering if your internet connection is flaky. (Too many bad nic's in my past..., I know.)
I'm going to give you the same summary of troubleshooting docs that I've assembled for other folks. Sorry I have to run...
anti-spyware apps - Do you have any running? Can you try opening iTunes while they are turned off?
malware - Have you run an anti-spyware app (Ewido seems to come highly recommended) to try and clean out any unwanted programs?
Norton Security, though I have run it with iTunes okay.
A bad installation, which might be corrected with a complete uninstall of iTunes and Quicktime, followed by a re-boot and a re-install. Also search the boards for standalone to see strategies dealing with correcting a bad install by installing the standalone version of QuickTime.
And
http://docs.info.apple.com/article.html?artnum=93976
Conflicts with other programs launched at StartUp. See the note at Apple about using msconfig to suspend the launch of programs at startup and identify any potential conflicts -
http://docs.info.apple.com/article.html?artnum=302538
And this thread
http://discussions.apple.com/thread.jspa?messageID=1163105� contains information about a specific piece of malware that interferes with iTunes and a link to a thread on removing it.