Need help to get rid of white space on top and bottom of content on home page

Look in your css files.

It seems all your .block elements have a margin at the bottom.

Just delete that or target the elements specifically in css and remove the margin.

line 133 of html-reset.css:

h1, h2, h3, h4, h5, h6, p, blockquote, pre, ul, ol, dl, hr, fieldset {
    margin: 1.5em 0;
}

That 1.5em vertical margin on a paragraph is causing most of it.
The real issue is not the CSS, but that you have an <iframe> inside a <p> tag.

Maybe use a different input format on your node?

In layout-fixed.css CSS file

If you change this:

#navigation {
float: left; /* LTR */
width: 100%;
margin-left: 0; /* LTR */
margin-right: -100%; /* LTR */ /* Negative value of #navigation's width + left margin. */
padding: 0; /* DO NOT CHANGE. Add padding or margin to #navigation .section. */
height: 3em; /* The navigation can have any arbritrary height. We picked one
that is the line-height plus 1em: 1.3 + 1 = 2.3
Set this to the same value as the margin-top below. */
}

.with-navigation #content,
.with-navigation .region-sidebar-first,
.with-navigation .region-sidebar-second {
margin-top: 3em; /* Set this to the same value as the navigation height above. */
}

To this:

#navigation {
float: left; /* LTR */
width: 100%;
margin-left: 0; /* LTR */
margin-right: -100%; /* LTR */ /* Negative value of #navigation's width + left margin. */
padding: 0; /* DO NOT CHANGE. Add padding or margin to #navigation .section. */
height: 1.5em; /* The navigation can have any arbritrary height. We picked one
that is the line-height plus 1em: 1.3 + 1 = 2.3
Set this to the same value as the margin-top below. */
}

.with-navigation #content,
.with-navigation .region-sidebar-first,
.with-navigation .region-sidebar-second {
margin-bottom: -2.5em;
margin-top: 1.5em; /* Set this to the same value as the navigation height above. */
}

It should be fixed. You can change margin amounts and can use px instead of em. I did not inspect any possible side effects of this change and tried only in Firefox 11.0.