How can I create *.rul*file for topology in ArcGIS?
In ArcCatalog, create a topology on a feature dataset in a database. In the New Topology wizard, when you're asked to add or remove rules, you can save the ruleset which will create a .rul file.
ArcEditor and ArcInfo only...
Creating Topology (ArcCatalog) http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Creating_a_topology/006200000005000000/
Useful PDF (for all the types of topology) http://help.arcgis.com/en/arcgisdesktop/10.0/help/001t/pdf/topology_rules_poster.pdf
Exercise 9 of this PDF http://webhelp.esri.com/arcgisdesktop/9.3/pdf/Building_Geodatabases_Tutorial.pdf will guide you through the process (9.3 version)