The whole point to NetObjects is that it uses fixed pixel dimensions to ensure that your page elements (buttons, navigation, banners and content) remain in the same position on the page relevant to one another regardlesss of page resolution.
The simplest workaround I can think of for you is to create a table on your NetObjects pages where your content will go. If you give the table the correct parameters it will size to browser window but your page layout will not suffer as a result since the page elements will still be bound by your Master Border and Layout.
In NetObjects 7, this is from the helpfiles under the section Working with text boxes, "Creating Pages that Resize to the Browser Window":
You can configure NetObjects Fusion so the text box is maximized in the site visitor?s browser window. When you use this option, NetObjects Fusion generates the page?s HTML without using tables.
1 In Page view, click the MasterBorder.
The MasterBorder Properties palette appears.
2 Select the ZeroMargins MasterBorder from the MasterBorder name drop-down list or use any combination of AutoFrames and non-framed MasterBorders with margins set to zero.
3 Select an existing text box or create a new one and embed all objects in the Layout area in the text box.
4 On the Text Box tab of the Text Properties palette, select Size Layout to Text and then Contents wrap to browser width.
When you publish this page, the contents of the text box adjust to the size of the browser window.
And this is from the "Publishing with dynamic page layout" help document.
When you choose Dynamic Page Layout, NetObjects Fusion uses complex hidden tables to achieve the highest level of layout accuracy across browsers. To see the table borders in your browser, hold down Shift when you click Preview Site or Publish Site.
Dynamic Page Layout is the default publishing method for NetObjects Fusion. Using Dynamic Page Layout:
· You get relative placement of your content as you designed it in Page view, with relative spacing preserved regardless of the site visitor?s display configuration.
· You can prioritize the vertical relationship between objects so site visitors are more likely to see the pages as you designed them, regardless of their local browser, font, and display configurations.
· Pages can be viewed in most browsers that support the 3.2 HTML specification, including Microsoft Internet Explorer 2.0 or higher and Netscape Navigator 2.0 to 4.x. Netscape Navigator 6.0 does not support this option.