a) CSS is the only way to widen benevolence.
b) There are only a few here in the forums with any CSS experience, and they are only here randomly, so you really should have some knowledge of CSS and how it relates to the markup (HTML) or it can be quite frustrating.
The one thing to remember is that there are still a fair amount of people out there using 1024 x 768 resolution, which means the overall width of your theme should not exceed 1000px (and I prefer to stick with 990px max just for a little breathing space). Horizontal scrolling is the #3 thing out of 10 that people on the web don't like to do.
Delete everything in the CSS edit window (appearance > edit CSS) and paste the following into the CSS edit window and then click "preview".
#wrapper {
width: 990px;
}
#masthead {
width: 990px;
}
#insideWrapper {
width: 990px;
}
#content {
width: 690px;
}
.post, .page {
width: 690px;
}
#footer {
width: 990px;
}
There are other things that will have to be done, but this will give you an idea of what it will look like at 990px overall width. Basically it is an increase of 290px to the content area since I left the sidebar the same width and location.