Check the aolserver tcl api at
http://www.aolserver.com/docs/devel/tcl/api/conn.html#ns_connFrom the docs:
"ns_conn location returns the location string for this virtual server in the form: protocol://hostname[:port]"
In your tcl file, set hostlocation [ns_conn location].
In your adp file, display <a href="@hostlocation@/forums/">mesgag ba0rd</a> for the appropriate location.
[note that ns_info location is obsolete.]
You can also use relative also as has been mentioned (../forums, ../notes).
...might be a better way to do this. check the genius bar.