I don't believe there is a key command or special button for instantiating a software instrument. However after the software instrument is first instantiated, you can use the v key to toggle it's window open and closed.
To first instantiate a software instrument, you need to double click on its name in the channel strip. The instrument's name appears in a little rectangular box slightly above the fader. It's highlighted in blue. That's where you double click. You can now close the instrument's window with the v key and it will open again with another press of that key. The v key behaves this way for any software instruments and/or plug-ins that are open. If you don't want a certain window to keep opening and closing with the v key, just close that window by clicking on its close button.
Also, do you know that all macs have universal access features. They can be accessed through the system preferences. There is a zoom feature. You may have to go to system preferences to turn it on, but then you'll be able to zoom in on anything on the screen - it zooms right in to wherever your mouse is pointing - pretty neat. To zoom in, press option, command, and the equals sign. To zoom out, it's option, command, minus sign. I believe you can enable this feature by pressing option, command, 8.
Hope that helps,