Try this

"http://www.mapquest.com/cgi-bin/ia_find?link=btwn%2Ftwn-map_results&random=565&event=find_search&SNVData=&address=" + lc_street + "
&city=" + lc_city + " &State=" + lc_state + " &Zip= " + lc_zip + "&Find+Map.x=0&Find+Map.y=0"

where:
lc_street = "100 Main"
lc_city = "Anytown"
lc_state = "MI"

If the zip code is not known the omit the " &Zip= " + lc_zip in the string.

This was a "quick and dirty" by typing in an address at mapquest and copying the address form the browser when the map appeared. I ahve not actually tried this in VFP.

Hope this helps.