need help with users roles

Hi,
I have just downloaded the sql server 2008 version. I am currently developing a web application which is to be uploaded on the internet Now the web application and the database both will be on the same site .To be precise I am new sql server, whenever i try to run the website ,the login page comes perfectly but when I try to enter the id and password it shows me an error that :
Login failed for 'userGuest'.
I think(but not sure) that this is sql server error and might be caused because of some roles or logins.
Can any one please help me with the problem that is am I correct , is there a way to resolve it
i am giving You the screenshot of the error here:
http://lh4.ggpht.com/_EC8qUhn9kJY/Sq4yFPLtvEI/AAAAAAAAAGA/Bt_L1eKpI7c/error.JPG

<p>&nbsp;HI,<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px;"><div style="margin: 8px; color: rgb(0, 0, 0); font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 12px; background-color: rgb(255, 255, 255);"><p>I thank to all of YOU who tried helping me out&nbsp;</p><p>the problem was later solved by me as I was using integrated security=true which should have been false.<img src="http://forums.asp.net/tiny_mce/jscripts/tiny_mce/plugins/emotions/img/smiley-wink.gif" mce_src="/tiny_mce/jscripts/tiny_mce/plugins/emotions/img/smiley-wink.gif" alt="Wink" title="Wink" style="border-width: 0px;" border="0">&nbsp;in case of sql server authentication.</p></div></span></p>