Hi Richard Brown,
Version 2.0 of Telerik Reporting is backwards compatible and all reports created with the previous versions should work as expected. The only difference is that TextBox.CanGrow is now true by default. For more information what's new please see the Release History
Regarding the margins in the Web Viewer -- since the viewer renders the reports in HTML and it is not page oriented format the page settings are ignored. This includes the margins too and Web Viewer just shows the report in the center of its viewing area.
In case you have found any other discrepancies between the 1.5 and 2.0 version please send us your report and any other information you find useful so we can examine it and give back to you with proper solution.
the Telerik team