In your open document in OpenOffice.org:

Open the Stylist by using the drop-down menus, Format > Stylist or Styles and Formatting, or by pressing the function key, [F11].
In the Stylist window, click on the Page Styles icon (fourth icon from left).
The type Standard or Default will likely be highlighted. Hold the right mouse button down to see the context menu and choose New...
In the dialog that appears, give the new page style a descriptive name, such as Landscape Page.
Click on the Page tab and change the page orientation to Landscape by clicking on the adjacent radio button. You may also make other changes you wish to assign to this page style, such as adjusting the margin sizes or enabling the header and footer.
Click OK. The new style will appear as one of your page style choices.
Place the text cursor in your document at the location where you want to insert the Landscape page.
Select Insert > Manual Break...
In the dialog that appears, select Page Break and in the Style drop-down list, select your new page style, for example Landscape Page.
Click OK.

To end the Landscape area in your document:

Place the text cursor in your document at the location where you want to stop the Landscape layout.
Select Insert > Manual Break...
In the dialog that appears, select Page Break and in the Style list, select the previous page style, such as Standard or Default.
Click OK.