interface the Arduino with Excel
You can't do the because the arduino doesn't write files onto a PC.
What you have to do is let the PC program that the arduino is talking to write the Excel file.
This is very easy, simply write the text of the values you want separated by a comma and do a println to get a new line. If you call the file something.csv then double clicking it will load it directly into Excel. You can then save it as a fully fledged .xls file. In fact that's what I am doing now at work. The programming language is called Processing.
EDIT before you ask here it is:-
/**
* Generates some random numbers and stores the results in an output file 'Results.csv'
*/
PrintWriter output;
int index = 0;
void setup() {
size(200, 200);
background(0);
stroke(255);
frameRate(12);
output = createWriter("Results.csv");
for(int j = 0; j < 40; j++) {
output.print("Random Number ");
output.print(" , " + random(-5, 10.2));
output.print(" , " + random(-5, 10.2));
output.println();
} // end of 'for J' lines
output.flush(); // Write the remaining data
output.close(); // Finish the file
println("Generation finished");
}
void draw() { // nothing in the loop it's all done once in setup.
}