How can I create a street isocrone of 90 minute around an airport?

I need to describe the catchment area of an airport and I need to rapresent it with an isocrone of 90 minutes on the street network. A friend of mine worked with Accessmod 3.0 programme, but it work only on ArcView 3.2 and I don't have Spatial Analyst 1.1, wich is required.