Caps lock will do an instant zoom.  Very useful when you need to rapidly give different units orders to move to different destinations (such as scouts at the start of the game).  Unfortunately, caps lock won't zoom in to cursor, so you'll need to click on the planet you want to zoom in on.

The hotkeys are V and B, I believe.

Why not just get a wireless mouse and keep it in your laptop bag?  I can't imagine how difficult it would be to play this with a touchpad.  Heck, I don't even like using my laptop for Internet surfing (or whatever else I'm doing) without a mouse.

actually, if you go into the control panel's mouse settings, you should be able to set it up so that a small section on the right side of the touchpad is a scroll section. You'd also probably want to make it so that it functions on mouse-over instead of when the window has focus. I'm not 100% sure this will work, but it's a way you might get the zoom working on the touchpad.

getting a mouse is a good idea though