Input Validation

OK, I was wondering if anybody could point me to a good input validation tutorial that explains things clearly and concisely, or maybe could just show me the code.

I want the input to contain only a-z, A-Z, 0-9, ( ), - , as well as . and spaces. I sort of had my head around it, but then everything I read started appearing as a blurred jumble, so I'm a little confused, as always :)

Thanks for any help in advance.