I'm assuming that when you say 'click the button, it moves to the top a little' you're talking about the mouse down click state for the button, and that when you release the mouse click, it returns to its normal state? And that you're disabling the default rendering of the button by using:
input, button, submit { border:none; }
If so..
Personally, I've found that you can't actually stop/override/disable this IE native action, which led me to change my markup a little to allow for this movement and not affect the overall look of the button for the various states.
This is my final mark-up:
<span class="your-button-class">
<span>
<input type="Submit" value="View Person">
</span>
</span>
This CSS Buttons tutorial is the article I referred to to start the above, but as you can see, I had to amend it to support the input button.