The Select button is a <input type="button"> element and you can style it using the ruBrowse
As you might already know, there is a transparent <input type=file > element above the textbox area and the Select button, so you might face problems trying to handle let's say hover event - because that event will be fired from the transparent file input, rather than the Select button.
Here is a small trick on how you can handle the mouse over the input element and change its background with another image. Add this CSS rule to the <head> section of your page:
| background:transparent url('images/Your_New_Image.gif') 100% 0 no-repeat;
is the name of my skin.
All the best,
the Telerik team