I am putting this link in - as a reference for anyone who wants to get the arduino to send data to an Excel spreadsheet.
please pay particular attention to the one line of the code that needs to be modified if your serial port number is greater then COM4 - i didnt, and struggled !
I have recently started using this myself to get the outputs from 4 thermocouples - upto 1100 degC ( via a Ryan j Mclaughlin arduino shield ) - got great graphs now !
There is also a ready-to-use free solution. It is based on PLX-DAQ software from Parallax:
It is easy to interface with Arduino and you can set the serial post speed up to 128.000 byte/sec !