Your original posting was rather lacking in useful information. You simply said Campaustralia and did not specify the actual URL you were using. I assumed, incorrectly, that it was campaustralia.com The .AU at the end makes a BIG difference. When posting a qustion to any support group, it is wise to include all the pertitnent infpormation.
Other information NOT included was which Safari and OS X version you are using, what changes you may have made in the interveening time period,like new OS version, rebuilds, other updates, configuration changes to your system and such, all might play a part in the problem.
Have you restarted the system at anytime since the problem has happened? Sometimes a restart can cure a number of oddball problems. That would help to indicate if the computer did have some "hiccup" in its operations. If it does the same thing (404) after a restart, then the problem is almost cartainly NOT in the computer barring somthing getting into some (usually hidden) system files. This would be very highly unlikely, especially if you are able to access all other web sites without a problem.
When you used the Microsoft OS notebook did you manually type in the URL? or did the Notebook fill in the URL for you from cached information? Is the URL used in the Notebook EXACTLY the same as the URL shown in your Safari window? The addition or lack of a "/" or a "." can make a difference.
Did you try using Firefox, Chrome or Camino as your browser? If so what was the result? What is the EXACT URL you are using that appears in your Safari browser window before you hit "return"? What exactly is said in the 404 error page you recieve? I mean the full text.
Like Don Archibald shows in his posting, the httpS header is treated differently than a http header. The "S" indicates it is a secure transaction. This is normally used for financial or other transactions where you wish only the recieving party to be able to decode your information. It is handled differently by the receiving server than the way a http header request is handled.
Also, like Don mentions, a 404 error is generated SOLELY in the server. What the server is seeing from your request can not be identified or located be the server.
Sorry that you do like to hear it but everything shown so far in your postings continues to point to a problem with the request the server is receiving from your system.