Could be a few things...
To start with, I can connect "mpfull.exe" to a couple of programs:
Windows Media Player, and
But not sure why they should cause problems (If it is even to do with those).
Have you/she tried installing Sims on another computer?
I know someone who is having a simular experience, she just says she can't install Sims, she keeps getting error messages. I am going over to sort
her out next week, it'll be funny if it's the same error message.
Maybe try a different Sims installation disk? Then if that works, take your copy back and get a new copy. If you have not got that option, just fork
out for a new copy.
I cannot really give you much info from the top of my head. If I come accross some more info I will post it here.