was going to tell you to read the manual, use the search function and try a tutorial myself......... (figured it would sound snarky

I guess Apple are "snarky" to even consider bundling the user guides with their software - how dare they show such lack of patience and understanding of their customer's concerns - LOL LOL!!!!!
I have found over the years, that when one gathers info for themselves - they remember it. When spoon fed, they come back a week later asking the same question again.... without any increase in their levels of understanding of the topic....
I think that in order for Dean to get to the bottom of this - it is lovely that we are to help and advise but - it is on Dean's computer, in Dean's house / office and our advice can only be up to a point....
I think that with what has been repeated here, that Dean has enough info to garner that A. he is doing something wrong or B. that he needs to reinstall FCS...
Good luck with it Deano -
OOOOOOH - one more piece of "advice"..... hopefully this one won't be deemed too "sharply critical; cutting" by out Moderator.
1. Take your sequence that you're working on - duplicate it and rename the duplicate TEST EXPORT (or something similarly applicable)....
2. Now open the Test sequence (double click it) and delete pretty much all of the timeline - BUT LEAVE ABOUT 20 SECONDS OF CLIPS AND AUDIO.
3. Now export THAT file and try getting a DVD out of it.
The point here is that such a small file will take "no" time to go through your system - so by logging what you doing, you will find the correct workflow very quickly....
Presently you are waiting too long for a very large file to wind it's way through your computer... so by the time it comes out on a DVD, the chances are likely that you've forgotten what you did.... (I do!!) So by testing your workflow on a nice short sequence, you should have the answer to your questions within 5 minutes...... you SHOULD have!!!
I would advice that you use a "difficult" part of the sequence with lots of fast shifting pixel data - i.e. something hard for the computer to compress - i.e. u/w and with some cross dissolves if you are using any.... The reason being so that you can check whether your encoding is being respectful enough of all of your pixels....
Hope you get through it today! This is TOOO long for a Mac "problem" to be going on..... 
good luck buddy