<p>I am just starting with SL and WPF. I am using the DataGrid control and I need to remove the mouseover effect (I actually will need to do more customizations than that). How do I do this. I think I need to do it with a control template but not sure how. I'm researching and reading right now. Any help would be appreciated.</p>

Yeah You have to change the Style and ControlTemplate , But are you using experssion blend to edit XAML? Blend is the easiest tool to do this.
Try changing the ControlTemplate for a Standard Button or ListBox and once you are comfortable then go to DatGrid. Why I am suggesting this is DataGrid is a complex combination of different UIElements so the control template will be hard to understand for a beginner.
Specific to MouseOver effect removal - There will be a
VSM
tag in the control template which has some storyboards , just remove the one with
```
<vsm:VisualState x:Name="MouseOver">
```
and you are good to go.