[REQ] Protection Code

I need a code that if users type in the following characters: '[];{}$ in text form, that it stops them and says: "Please use letters only."

I made one for myself, but it never worked. I really need this. :/ And mysql_real_escape or what-ever it is doesn't seem to work. Thanks!

This isn't a free coding service. Post what didn't work and perhaps someone can help you fix it.