iTunes 10.1 64bit on Windows 7 Ultimate x64 has bug it freezes iPhone 3G

I am using Windows 7 x64 Ultimate (Traditional Chinese) and I was using iTunes 10.0 for a few months without any problem. A few days ago, when I want to upgrade my iPhone 3GS to iOS 4.2.1.
I upgrade the iTunes to 10.1 64 bit and found out it freezes when it startup at the first time. after a while, it looks okay and I was able to play the MP3 etc... however, when I plugin my iPhone 3GS (with 3.1.2 firmware) into my PC. it freezes again. I already tried to reboot my PC several and it still doesnt work.
I thought it might be my iPhone need to upgrade to iOS 4, so I use my friend PC to do the upgrade. Now, my iPhone is at iOS 4.2.1. however, when I plugin the iPhone back to my PC, the iTunes still freezes..
I tried to uninstall all the apple softwares and re-intall the iTunes 10.1. it still doesnt work.
I also tried to reinstall the older 10.0.1 version; however, the iPhone iOS 4.2.1 cannot work with 10.0.1 version.
I am now in a dead-end and feel very frustrated..... could any one helps?
I am using the avast anti-virus, could it be the root cause? but, it works well with iTunes 10.0 before
Message was edited by: r390gt1
i5 Windows 7 x64 Ultimate Traditional Chinese