Centering form on web page

I have another question about centering my form on the html page (or hould the form be on a .php page??) I am submitting the information first to an page where they can edit any errors, then submitted to an SQL database using php. In any event, I have a sidebar to the left along the hieght of the page, with the following css;

#greysidebar {

float: left;

margin-top: 0px;

width: 80px;

height: 5000px;

margin-bottom: -5000px; /* any large number will do */

background-color: #999;

padding: 0px 10px 15px 20px;

} 

Would the form.css need to be changed, and what would those settings be? 

Do you have a link to the web page in question? We will need to check the layout to be able to help. Also, do you embed the form using a form source code method?

Thank you.