Richard made this program to synthesize a piano string available for people to experiment with for free!
He would like some help updating the model so it can simulate a "prepared piano," so if you can help him, get in touch with him. You can see his email address on this page:
Richard's Piano script is based on Master's thesis work by Charalampos Saitis which you can find at http://www.music.mcgill.ca/~harry/pdfs/Ch_Saitis_MA_Thesis.pdf .
Also, if you don't have Matlab, try out GNU Octave. It's free, very compatiable and quite good!