Styling email Form acknowledgment

[#1]

Hi there, I'm using the email form supplied by Plusnet and it's working perfectly. I want to style the standard acknowledgment page that the form generates. This appears when the user has used the form to send a message. It's a very ugly page and I want it to look like the rest of the site. Plusnet support have replied to my question by saying 'It would simply be a case of editing the files used for the web form' - which I knew to begin with. My problem is how to get to these files...does anyone know where they are stored?
Thanks

[#2]

If I remember correctly, it's just a case of adding something like

<input type=hidden name="redirect" value="http://www.username.plus.com/foo/bar.html">

to the form you use to call the homepages script. Then bar.html can be whatever you like.
Gabe