I'm testing Oblivion after a minor hardware upgrade; I haven't been able to play in a couple years or more. I've forgotten everything:

Can I remap the mouse 3 button as the Activate control?

Can the mouse wheel be used for anything other than changing the third-person view distance?

Thanks!

I'm pretty sure it can, you just have to have a try. Go into the controls section, select 'Activate' and click your Middle Mouse Button.

Well, yeah--I tried that first, but nothing happens. The game doesn't seem to recognize the middle mouse button. Are mouse buttons 1-3 reserved, exempt from mapping?

You can change the mouse mapping, I changed most of mine from the defaults. It did not reverse any of the buttons for me, including the middle button. Maybe it is your mouse?

In the options menu, select the Controls menu. In that menu there should be a button at the bottom left labelled 'Controls', click on it. That should bring the customizable controls menu. At the top where it says 'Keyboard' click on the right or left arrows beside it so that where 'Keyboard' was should now say 'Mouse'.
Set the controls to how you wish, but AFAIK scrolling the mouse wheel is hard coded to changing third-person view, you cannot change that.

Yep, i remember i couldnt remap the middle mouse button as well.