Forums Scripts & Popups $replace and etc...

I was wondering how could i replace everything in text exept the volews...

Example:

If i entered: Hello everyone
it would return: *e**o e*e**o*ne

And also is there an easier more suffient way of replacing all text and chrs with * in that... i cant just do $str(*,$len($1-)) because then it would be one line..


Thanks