The following XAML will give you the effect you are looking for.
Note that I have doubled the DLU units in the markup - thus keeping the same aspect. It looked funny having a Button height of 14units. You may need to tinker with the figures presented in the market.
Also, I started to remove some of the "Vista Layout" into separate styles. You may be able to continue down this path so you have quite a reusable set of styles which follow the Vista guidelines. I'm fairly sure some other people have done something similar.
Furthermore, I took some liberties with the size of the dialog. You mentioned you wanted 210x96units - you would need to set this amount, plus the window chrome.
Anyway, on with the content:
<Window x:Class="VistaLayout.Dialog"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Delete File"
ResizeMode="NoResize"
Height="212" Width="430">
<Window.Resources>
<Style x:Key="FooterButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Width" Value="100" />
<Setter Property="Height" Value="28" />
<Setter Property="Margin" Value="8,0,0,0" />
</Style>
<Style x:Key="FooterPanelStyle" TargetType="{x:Type UniformGrid}">
<Style.Resources>
<Style TargetType="{x:Type Button}" BasedOn="{StaticResource FooterButtonStyle}" />
</Style.Resources>
<Setter Property="Rows" Value="1" />
<Setter Property="HorizontalAlignment" Value="Right" />
</Style>
</Window.Resources>
<DockPanel Margin="14">
<!-- Footer -->
<UniformGrid DockPanel.Dock="Bottom"
Style="{StaticResource FooterPanelStyle}">
<Button>_Yes</Button>
<Button>_No</Button>
</UniformGrid>
<!-- Main Content -->
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="8" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Image Width="64" />
<StackPanel Grid.Column="2">
<TextBlock Margin="0,6,0,14">Are you sure you want to move this file to the Recycle Bin?</TextBlock>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="14" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Image Width="60" />
<StackPanel Grid.Column="2">
<TextBlock>117__6.jpg</TextBlock>
<TextBlock>Type: ACDSee JPG Image</TextBlock>
<TextBlock>Rating: Unrated</TextBlock>
<TextBlock>Dimensions: 1072 × 712</TextBlock>
</StackPanel>
</Grid>
</StackPanel>
</Grid>
</DockPanel>
</Window>
As with most XAML, this could be done in a myriad of ways - this is only one solution.
Hope this helps!
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…