Simple Twety Ten Layout Problem

you must have done other changes at the same time:
for instance here:

#container {
	float: left;
	margin: 30 -240px 0 0;
	width: 100%;
}

needs to be 30px

also see:
http://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Frippedandtorn.co.uk%2Fissues%2Fissue-4%2F&profile=css3&usermedium=all&warning=1&lang=en

there is another error here (without any visible effect):

#wrapper {
	background: #fff;
	margin-top: 20px;
	padding: 0 20px;
	background-image: bgcross.jpg;
	background-image: url(http://rippedandtorn.co.uk/images/bgcross.jpg);
}

remove this: background-image: bgcross.jpg;

btw:
twenty ten as the default theme of wp3 will be overwritten with the next update of wordpress, and all modifications will be lost.
therefore it is advised to create a child theme: http://codex.wordpress.org/Child_Themes