I have the same problem. I let Internet Explorer 7 handle the problem
What I do is the following.
I set the interactive margins of the report to 0,0
I remove any body margins.
I set the paper size to A3 landscape
Then I run the report in Internet Explorer 7
I change the "preview size" in the reporting bar to "whole page"
Then I do a right click on the report and select "print preview"
I make sure that it is "shrink to fit"
That the page setup (4th button on the left) is set to A3 and landscape
And then print