In ArcView 3.x, there was a transparent symbol in the Symbol Palette. In ArcGIS 9.x, a user needs to load a special toolbar to symbolize features as transparent. In addition, a user can change the brightness of an image using this same toolbar.
Go to View > Toolbars > Efects to load the Effects Toolbar
* Choose Lakes under Layer
* Click the Transparency button and move the slider bar to 50% You will see the municipal boundary through the lakes now
* Check on the MrSID in your TOC
* Choose MrSID under Layer in the Effects Toolbar
* Click on the Brightness button and adjust up and down. You will see the image change