Setting which layers are selectable in ArcMap?

In the Table of Contents window, there is a button across top titled "List By Selection". Clicking this button toggles the Table of Contents into a mode that lets you change the selectablity of each layer in your dataframe.

You probably already figured this out, but in case someone else comes across it, you can click the small selection icon to the right of the layer you want to make selectable (or not selectable). See the red arrow:

check this link

http://www.geocortex.com/about/blog/archive/setting-selectable-layers-in-arcgis-10/

The "Set Selectable Layers" option is still available in ArcGIS 10, you just need to add it like you would a custom tool:

Click the Customize menu > Customize Mode > Commands tab. Type "set selectable layers" in the "show commands containing" search box, and drag and drop the Set Selectable Layers command on to your Selection menu.

set selectable layers