iTunes 8.2.1.6 - Memory leak?

I upgraded to the latest iTunes recently and the application has become unusable. When I click on any a song, a menu item, or anything, there is always a 5-10 second delay before the item is even highlighted. No "beachball", nothing. Using Task Manager I can see that iTunes starts off using 58MB of RAM, but slowly builds on that, even when the application is in the background and not playing any music. The used RAM never drops. I came back from dinner tonight and it had reached 356MB.

I have tried completely uninstalling and reinstalling iTunes, but there was no change. No other applications are affected, only iTunes runs impossibly slow.

System details:

Windows Vista Ultimate 64-bit
Intel Core2 Extreme CPU Q9300 @2.53ghz
8GB RAM
12,941 items in my iTunes library
No playlists (I had five small lists before I reinstalled)
iTunes library stored on external USB drive, mapped to F:\iTunes

The previous version of iTunes worked without issue using the exact same configuration. The only change was the iTunes upgrade. Is there a link to somewhere I can download the previous 64-bit version? As I stated above, the current version is 100% unusable for me.