Here are afew lines from a tool I have written in the past. This explains populating a field/control with eastings and northings base don whether the user map clicks or uses the GPS. It doesn't answer your question about lat and long, but I'm sure it's possible...
If Application.UserProperties ("AddPoint_ToolUsed")="addpoint" then
objEFPageOneControls("EASTING").value = FormatNumber(Map.PointerX,2,-2,-2,0)'FormatNumber(Map.PointerX,2)
objEFPageOneControls("NORTHING").value = FormatNumber(Map.PointerY,2,-2,-2,0)'FormatNumber(Map.PointerY,2)
Application.UserProperties ("AddPoint_ToolUsed")=""
else
objEFPageOneControls("EASTING").value = FormatNumber(GPS.X,2,-2,-2,0)'FormatNumber(GPS.X,2)
objEFPageOneControls("NORTHING").value = FormatNumber(GPS.y,2,-2,-2,0)'FormatNumber(GPS.Y,2)
end if