90 min footage to 4.7GB DVD?

I have circa 90 min footage to burn onto a 4.7gb 120min DVD, but I see from the forums that it isn't that straightforward to do!

I am using Premiere Pro CS3 (educational licence) in which I have created my timeline. I then use the "export to encore" which does what it says it will do, but when I get into encore and try to build the disc, the program halts and tells me the project is bigger than the media.

I understand that it is something to do with bitrates, and my video file is going to be 5.xgb in size, so won't fit.

What I don't understand, is how and more importantly where do I alter these files?

Do I do it in Premiere or in Encore?

And now you've told me that, please might I have an idiots guide as to how to do it??

Thank you in advance