Html email and php problem - php help please

ok here is my problem if anyone has time. I followed this simple tutorial and it works fine:

However i do have a question, when i fill in the form, and submit the enquiry, i get a white page saying thanks for posting etc etc. Thats all well and good, but what i really need is for it to open a page (that looks like all my other pages graphics wise) lets say this page would be called thankyou.html - I’ve seen this done many times on web sites so i know it is possible - but i dont know how.

i put my version online so you can check what i mean:

feel free to try it - i dont mind the emails:)

i’m also going to send the two files in a zip to save anyone willing to help some time.

Your help in this matter would be most appreciated.

thank you