Sun Microsystems's Star Office works and can be used at no charge, although whether it's open source depends on your point of view. Another free usable tool is EasyOffice from e-press.com. There are open source office tools available, and an effort is underway to build a complete open source desktop.
I wrote this column under Windows in AbiWord, a cross-platform Gnu Public Licensed word processor I downloaded from www.abiword.org. So far, so good. The file/save menu supports Rich Text Format (RTF), HTML, LaTeX and Palm document formats, but not Microsoft DOC. After saving in RTF, it's off to find a spreadsheet.
The open source desktop project is called GNOME (www.gnome.org). The GNOME-Office project site (www.gnome.org/gnome-office) promotes interoperability coordination and provides links to open source office applications, including AbiWord. Here I found a link to the cross-platform spreadsheet OpenCalc, included in OpenOffice from www.openoffice.org, which is available under a dual GNU Public License/Sun Industry Standards Source License arrangement in binary versions for Solaris, Linux and Windows. OpenOffice is being integrated into GNOME with support from Sun. You may lose some bells and whistles, and experience file compatibility conflicts with users of the newest Microsoft Office releases, but you'll be able to get the job done.