I'm not aware of any commercially available plug-ins for v2003 that
perform WAN discovery. The fluke tool that is available with the visio
resource kit is adequate for single site lan configurations (unfortunately
it is currently out-of-stock per MS, around $200USD).
https://microsoft.order-9.com/visiopro/
The Netformx tool (DesignXpert) appears to be an extended version of the
Visio VENT implementation and runs for about $1000USD. If your topology
really needs such a tool, not an unreasonable price.
http://www.netformx.com/solutions/entAuto.asp
al