Firstly, I see that my mvc3 project already had jquery ui but no css theme files.
I need a date selected and, as usual, to override EditorFor DateTime. I started from today, just using the default jquery ui js files supplied with the project under scripts. The date picker displays well, only with a complete corrupted Site.css based user interface.
So, now I downloaded the jquery assembly (with the start theme ) and after this page on how to build it.
I use T4MVC, so my page looks like this:
Layout.cshtml
<script src="@Links.Scripts.jquery_1_4_4_js" type="text/javascript"></script>
<link href="@Links.Content.Site_css" rel="stylesheet" type="text/css" />
<script src="@Links.Content.start.jquery_ui_1_8_7_custom_css" type="text/javascript"></script>
Create.cshtml
<script src="@Links.Scripts.jquery_validate_min_js" type="text/javascript"></script>
<script src="@Links.Scripts.jquery_validate_unobtrusive_min_js" type="text/javascript"></script>
<script src="@Links.Scripts.jquery_ui_1_8_7_custom_min_js" type="text/javascript"></script>
And this is the result:

, , script css , .
. , <script> <link> ! , css Site.css.

2:
, jquery css. fiddler, css.
!
<link href="@Links.Content.start.jquery_ui_1_8_7_custom_css" **rel="Stylesheet"** type="text/css" />
! , rel!