Actually, this raises an interesting question with respect to the IE specific conditional comments and whether or not they are a good idea. (I'm sorry that this has drifted a bit off-topic).
Browser detection won't work. Feature detection is better, and the abstractions in YUI and other libraries pretty much do most of the work for you.
However, where your requirements are restricted to the need to supply minor CSS modifications that are absolutely specific to IE6 (for example to cope with the incorrect implementation of the block width calculations, or the lack of a child selector), is it better to start poking around in the DOM of ALL browsers to establish the reported block width for a single element (or the property value you set with the child selector), or better to use the conditional comments that Microsoft has provided for the purpose to insert changes only with IE6?
