Is there a way, using CSS, to show borders in a table between columns only (not on the outer edges)?
Borders on tables are always a bit flaky. One possibility would be to add a border-right declaration to each table cell except for the ones in right-most column. If you're using any kind of table-spacing this won't work very well.
Another option would be to use a 1px high background image with the borders inside it, but that'll only work if you can guarantee the width of each cell at all times.
Another possibility is to experiment with colgroup / col. This had fairly horrible support cross-browser the last time i looked at it but could have improved since then: http://www.webmasterworld.com/forum83/6826.htm