From GPS it comes each second - just to clarify.You need to convert these values into your screen coordinates.The points in your excel sheet are floats, probably.http://en.wikipedia.org/wiki/Geographic_coordinate_conversion
http://www.cosports.com/index.php/tool/tools/home
http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html
Here is a general explanation:
http://www.csu.edu.au/australia/latlong/coord.html
http://forums.gpsreview.net/viewtopic.php?t=13651
You can verify yourself with it: http://www.gpsvisualizer.com/geocoding.html