The ad.tcl file which is used to parameterize your installation is referencing the Tcl variable "server", which you need to set up in your nsd.tcl file. It is set up this way so you only need to add that one line, rather than edit a bazillion hard-coded references in the ad.tcl script.
This is structured into two scripts largely for historical reasons. nsd.tcl traditionally is used to set up server parameters, database pools, etc and an example comes with the AOLserver download. This is a generic set-up file that isn't strongly tied to the ACS.
In contrast, ad.tcl is full of ACS-specific parameters.
There actually is some installation documentation that covers this stuff...
