Buttons appear narrower in IE8 vs. IE7

When I view my site in IE8 buttons appear with less width, than in IE7.
For example, this Login Now button appears longer in IE7. In IE8 the buttons’ left and right side look like this, for example: [LOGIN NOW]
In IE7 it looks like this, for example: [ LOGIN NOW ]

<input type="submit" value="[var.lang_login_now]" class="button-form" />

Do you have any ideas how I can make the button appear in IE8 the same as it appears in IE7? [LOGIN NOW] vs. [ LOGIN NOW ] ?

Also, these buttons have the same issue:

<input type="submit" name="purchase" value="Purchase" style="margin:7px 0" rel="gb_page_center[600, 635] ">

<input type="button" name="search" value="Credits" onclick="window.location.href='credits.php';" style="margin:7px 0">

<input type="button" name="search" value="Search" onclick="window.location.href='page/page=77';" style="margin:7px 0">


Do you this is PHP issue?
Absolutely not. Rather ask in the design section where you can get fast answer.