Just started a new job.  AutoCAD I am using now does not have LAYISO as a command.  Is this something I have to program?  How difficult is this?

I believe LAYISO became a native command in 2008. Before that it was an Express Tools function. So I think you need to install ET from the install discs.

As well as the Layer Isolate command it can also be useful in cluttered drawings to temporarily hide objects. Here's a link to a free routine that will do this for you:
Object Hide http://www.3dcadmax.com/FreeAutoHide.htm