IE7 Width problem

Apologies if this is an effin' newbie question, but after two days of searching, I'm stumped.

I'm using the Bluebreeze theme and everything looks peachy-keen in Firefox. On IE7, however, the page is consistently rendered just slightly wider than the window, creating a scrollbar at the bottom, no matter if I have the browser in a window or fully expanded.

I've tried tweaking layout.css to see if I could klutz my way through a fix, but every time I change a container width, it breaks the layout badly - even a single pixel change. For example, my current layout.css has:

#main-wrapper {
  float: left;
  width: 100%;
}

#main	{
  margin: 0;
}

.withleft #main {
  margin-left: 190px;
}

.withright #main {
  margin-right: 190px;
}

#sidebar-left	{
  float: left;
  margin-left: -100%;
  width: 174px;
  padding: 5px 8px 20px 8px;
}
#sidebar-right	{
  float: right;
  margin-left: -100%;
  width: 174px;
  padding: 5px 8px 20px 8px;
}

#sidebar-right {
  .margin-left: -190px; /* IE7 Fix */
}

* html #sidebar-right {
  margin-left: -190px; /* IE6 Fix*/
}

#footer	{
  clear: both;
} 

Is this a known bug in IE that I am too stoopid to find or is there a hack to layout.css to fix it? I've tried tweaking the IE fixes above with no luck.

Thanks

RB