Break the string into letters , create models for every letter and check if the first letter is A , create the model of the letter A at the possition you want , then check the second letter and create the second letter.
If you have a picture(sprite) in the 3D world and you want the name of the player written in there use pixel drawing over a bmp image. Check in the manual for this.

PS.: Its hard to do theese two things if you are new to C-Script , so if you are , I suggest you try more simple ways , like a 'text' or draw_text command.