You don't say whether you are using a coding program like Dreamweaver or FrontPage but I think you are.
The solution seems to be applying a class to the p tag that you want to be different.
For people not using a coding program it would be:-
HTML markup in the body:-
<p class="nospace">Paragraph with different margins.</p>
Style in style tags in head section or in a stylesheet:-
.nospace { margin: 0 0 5px 0; } or whatever margins you want in the order top, right, bottom, left.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.