I recommend using em instead of px (eg. 20em instead of 20px) - it looks better that way using IE. If the font still looks weird, your best bet is to try using another font... or try using italics - it worked once for me.
Answer: no. You'd have to tell your visitors to turn on Font Smoothing, or to turn off ClearType (ClearType makes text less blurry and therefore more readable... but also gives you the jaggies). I've seen some IE filters that help undo ClearType for those who have it on... I wouldn't bother. And usually other browsers on Windows have an even worse case of the jaggies. This is something the visitors would have to deal with themselves since its their browsers doing it.
Maybe try the different default fonts? IE comes with like 6 or 7 fonts by default, there should be one or two that look decent. Verdana usually looks quite smooth and nice and it comes on IE.
no i havent heard of one, ie 6/7/8 has smooth font aliasing, other than that try using a true type font
have you tried @font-face which renders the font from the web server ( your site ) and supported in most browsers?