Propably easy regex question

Hi Could anyone help me with a code snippet that would take a string and add '> ' to it at the start of every new line just as a mail client does when replying to a mail? I.e. I would like this: Hello, How are you? To look like this: > Hello, > > How are you? When it's done. (Actually I would love it if it would also look for existing > at the beginning of a line, and if there are any, just add the > and not the white space but perhaps thats too much to ask for ;-) Thanks! - Nille