Thanks r0bb0b and nav33n however im not quite sure what to do with the code.

presumerably i put it at the beginning of the php script to make sure that it changes all strings with an underscore to have full stops instead however im not sure what $key or $value are meant to be.

I have a domain name field called "domain" and checkboxes for domain suffixes to be checked called "top_". its the domain field where the underscores need to be changed to fullstops

thanks again