I use Opera 7.0 with a microsoft mouse and have no problems. However I did find the following from the Opera help site that may assist.
"If you are using the Microsoft Intellimouse Explorer and cannot use the navigation (back and forward) buttons with Opera, please update your drivers to the latest ones from the following URL:
www.microsoft.com/hardware/mouse/download.asp"
Slightly adrift of your problem but I have downloaded and installed the latest drivers for my mouse so this may resolve your problem as well. Worth a try.