Woogyboogy, you have to set up a chat thread for each of the individuals you are wanting to change the options for (simply sending them a test text message will add a chat thread for them on the program's main screen)
then just open the chat thread and tap on the top right settings button within the contact's thread and it will give you options that are only applicable for that particular contact. Doing this you can change the font/font color, bubble color, background color, notification icon, led color on some phones like the droid, and what you were looking for, the text ringer =)
This is using Handcent as an example, i have no experience with other chat programs. I have been using Handcent SMS on both my droid and my incredible and they update often.