Do you mean, choose a sound when that person sends an instant message to you, or when you recieve an e-mail from him/her?
Be more clear in your suggestions please!
A certain sound when you receieve an email (into your hotmail inbox). I know Plus! can already use contact notifications for instant messages (which I have set up).
Like when you recieve an email from Bob for example. Bobs email is myemailaddress@hotmail.com. His "From" name is just Bob. Have the script play the sound when an email from "myemailaddress@hotmail.com" is recieved or when an email is recieved from sender "Bob".
Just when Plus! notices the messenger toast would be great. Sees the toast about a new email, scans who its from. If the email is in the list of custom sounds, it plays it. If not, the default sound is played.