Like extensions, templates have been slow to appear for OpenOffice.org, but are finally starting to become more readily available. Many of the collections mentioned here welcome new contributions, so ...

Open the spreadsheet in OpenOffice Calc. Click and drag to select the range where the hidden rows are; alternatively, press "Ctrl-A" to select the entire Calc spreadsheet. Click the "Format" menu ...

I've written in the past about places to find add-ons for Microsoft Office, but there's also a wealth of free extensions and templates for OpenOffice.org's Writer word processor, Calc spreadsheet ...