How to generate perpendicular lines to stream centerlines at points?

I have been searching for a way to create perpendicular lines at the midpoint of each small stream segment so as to get 3D cross-sectional transects. I have found this script but it's out of date and doesn't work for me. It describes exactly what I want to do but can't: http://arcscripts.esri.com/details.asp?dbid=15756. also found a transect toolbox but it only will do them at intervals or at midpoints between vertices, not the midpoint of the entire line: http://gis4geomorphology.com/stream-transects-partial/

I hope to get the cross section geometry to build a dataset for the MODFLOW SFR package.

Dianne Yunker
Arizona Department of Water Resources
Modeling Section | Hydrology Division
Phone: 602.771.8415