Start by using the code validation tools below and fix any reported errors.
Well, I do get a boatload of statements like this one
21 table.sample th Property -moz-border-radius doesn't exist : 0 0 0 0 0 0 0 0
telling me that it can't find the style.css file?
So, does that mean that Firefox has these references built in that IE doesn't recognize?
Border-radius is a recent addition to CSS level 3 standards. Some browsers support it. Some browsers like Web-Kit and Mozilla need proprietary tags to support it.
And still others like IE6, 7 & 8 don't know what border-radius is and probably never will.
These kinds of validation errors aren't crucial to your layout. So you can ignore them.