Form Validation

I need to validate a form in PHP. Here are the things I have a prob with. Checking if a field has only letters. Checking if a field has only numbers Checking if a field contails a valid e-mail address like someone@somthing.com Checking if a field does not have any special charecters like ~!@#%$^*() I also want to thank everyone who answered my question of how to convert lower case to upper case. SID