I'm not expert on PHP, but I think that is OK.
But to make it more readable, try an 'or'
<?php
if (is_page("stills")) or (is_page("anotherwidepage")) {
echo "<div id=\"right-column-no\">";
} else {
echo "<div id=\"right-column\">";
}
?>
Untested.
PS. To be clear 'right-column-no' is a style in the style sheet that looks like this:
#right-column-no {visibility:hidden}
and there is another style called by a similar if else:
#left-column-single {width : 800px;float : left;padding-left:40px;}
I just took the 300px width of the right column and added it to the 500px width of the left-column format.
This is not a general solution, that is, it will depend of the particular theme. This is for the 'A Dream to Host' theme.
And not an easy scheme to maintain if you add pages, either lots of work, or one forgets how they did it. I try to put notes about changes like this in a private or unpublished page. Hoping someone will have a better solution