You seem to want to have your custom solution and in that case you need to write your own code. If you use Processing it will allow you to log the data directly either into a .txt file or a .csv (comma separated values) file which you can open with Excel. Its really easy and there are examples out there. Processing has a powerful instruction (PrintWriter) that allows you to do that really easily. The only problem is that you can't do the graph in real time if you log the data into Excel (or I don't know how to do that yet). After the data is logged in, then you have to manually set the graph in excel. I have done it and works just fine.
-Send the data from Arduino to Processing using the Serial communication library. There are tons of examples out there.
-Write the data into a .txt file or .csv if you want to use Excel and all its possibilities. For that you use PrintWriter.
PrintWriter datalogger;
datalogger=createWriter("datalogger.csv");(If no path is specified it will create the file in the sketch data file. If not, in the folder you specifiy the path for)
datalogger.println( data1, data2, data3,....,dataN); (writes data into different contiguous excel cells).
datalogger.println(); leaves a blank line of cells (not filled with data whenever you want).
datalogger.println(moredata, evenmoredata, extradata);
-Flush the data every once in a while in your code (on every Procesing loop or so).
datalogger.flush();
-Close the .txt file or .csv file at exit.
datalogger.close();
exit();
You can use the same thing with a .txt file; but to read the data back and make graphs will be a bit more complicated requiring loadStrings() into arrays and convertions to float(string);
If you want multiple files simply use arrays, like this:
PrintWriter []datalogger;
void setup()
{
datalogger=new PrintWriter[NumberOfFilesYouWant+1];
for (int i=0; i<NumberOfFilesYouWant+1;i++)
{
datalogger=createWriter("datalogger["+i+"].txt");
}
}