Don't use CSS hacks, Javascript to switch style sheets or anything like that.
I've never ever had to use multiple style sheets for different browsers or any invalid CSS hacks.
Its not needed. The conditional comments are useful for maybe IE6 and below for the PNG fix stuff, but appart from that, if you know CSS and the various browser bugs you can easily code XHTML and CSS for IE 5.5 without many problems.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…