There are a couple of ASCII compatible formats.
In File-->Save As there's a window called
"save as type" check the drop down menu for different options, the most ASCII friendly one (IMHO) is Text Tab delimited (easy to get back into an excel format). There's also Formatted text(space delimited-can screw you up if there are spaces in the data in your cells), CSV, as well as text and csv for mac or dos. Most of my experience is with tab-delimited, but you should play around with them and see what works the best for you.
So you'll have to make one ascii compatible file per worksheet, not workbook.