As I understand it, GE v.1.28 will have an "Input Actor" that will allow you to easily get a user's input. Until 1.28 gets here though, it is probably only through using C programming that you can create something that will proccess a user's input.
You might be able to come up with something by scripting something to get a user's input and then reading and writing the user's name to a file.
Here are a couple of threads that deal with reading and writing to files:
http://game-editor.com/forum/viewtopic.php?t=349
http://game-editor.com/forum/viewtopic.php?t=159
Unless you are pretty comfortable with C programming, I'd wait for the new version. It should be out soon. HTHs.