Thank you for providing a live URL.
We are aware of this issue with RadInput Mac skin. Unfortunately, it is caused by IE7 behavior (I can't tell whether this is a bug or not).
Because of this problem, we have already removed the textbox background images from RadInput Inox and Macromedia skins. However, the Mac skin is somewhat special and the textbox cannot be made look like a real Mac textbox without background images.
You have a couple of options - use a custom Mac-like skin with no background images, or use another skin.
If all you Mac skin textboxes are the same size, you can try the following workaround - remove the background images from the textbox and use them on the HTML elements containing
a RadInput. Thus these background images will not move with the textbox text. RadInput has client events, which you can use to change the CSS class of the control's parent element, so that the user experience (changing colors on hover, focus, etc.) is preserved. For example:
Let us know if you need additional information.
the Telerik team