This will allow the user to specify searching the subject or body only or both. It also allows specifying the username in addition to the search criteria and not as an either/or option.
This also provides the fix so that showflat.php and showthreaded.php display your multiple word search results all words are highlighted.
There seemed to be an error for me in dosearch.php where the line
if ($Searchpage 0) {
is used.
I had to change this to
if ($Searchpage) {
to make it work for me.
Give me some feedback on how this goes. It may need some adjusting.