I uninstalled all previous ReSharper versions EXCEPT ReSharper for VS2003 (2.0.269.2).
Reset all settings (via Tools -> Import and Export Settings -> Reset all settings).
Exited all instances of Visual Studio.
Installed ReSharper 3.0 RC 465.
Then started VS2005 and found that all ReSharper menus were disabled, there were no items in Tools\ Add-in Manager window, and there was "ReSharper 3.0 " item in Help\ About MS VS window.
I repeated uninstall\install with ReSharper 3.0 RC 465 and ReSharper 3.0.423 unsuccessfully some times, and succeeded only with ReSharper 2.5.370.