The previous code computing rowStart will fail when there are theads since tHead contents are also computed inside table.rows.
However, that code probably worked at some time, so perform a computation to ensure that table.rows isn't getting just the tBody contents.
Please cross browser test.
The last code version of this sortables is on
http://yoast.com/articles/sortable-table/ and has changed quite a bit. Joost de Valk suggest
using the jQuery based tablesorter.com.