Internet Explorer Font Problem

Not sure what kind of font problem you're referring to. You didn't say what kind of problem and you didn't specify which version of IE you're seeing these problems in.

There are just a few places in the form CSS that even specify font types - mostly simply defining a default san-serif font. There are a couple of places in the jQuery UI styles and the Thesis-specific styles where named fonts are specified but those are web-safe fonts as well.

If you're having any font-related issues, it's most likely coming from your theme styles and not the form CSS. The forms are intended to inherit most of the typography styling directly from the theme.

If you're referring to the small font size on the labels, I see those in several non-IE browsers. That's because line 13 of your style.css file is setting a blanket font size of 87% for all fonts. Most likely it's an attempt at a reset value. You can either remove that rule, or add a new CSS rule to make the label size 100%.