I have my bounds, and have been able to connect to the server http://imselev.cr.usgs.gov:80/wmsconnector/com.esri.wms.Esrimap/USGS_EDC_Elev_NED_3? in python. What I don't know how to do is send a request to download the area in arc ascii grid format. I would be grateful for any suggestions, examples, or pointers to where I might find examples.
WMS, by design, provides simple images (GIF/PNG/JPEG, etc.) of geospatial data. To get to the actual data, this would have to come from a Web Coverage Service (WCS).
As well, the WCS would have to support the format(s) you are looking for. If it doesn't, you could access the data in one of the formats is does support and then transform it locally.