The download for the current WEPP Windows interface is found on the main NSERL WEPP page.
The WEPP Internet version can be run by connecting to a server at the NSERL. Currently this version only has a few management options. The Internet version includes hillslope and GIS watershed applications.
Running the WEPP model within a GIS is available in Beta from Chris Renschler at SUNY Buffalo. This version uses an ArcView interface along with special programs to create WEPP model inputs from ASCII grid files.