I read Mr.Wolley article and he said-"I have almost exclusively used table widths of 580 to 595 pixels through out this site.when using static width tables,I recommend a maximum table width of 600 pixels"...

We all used to put margins say in MS word when creating doccument .

1.How can we translate it in webpage layouting?
2.How long does a webpage width of 600 pixel in inches?
3.Am planning a 3 vertical column layout-The first is for my navigational bar,
the content is in the center and the 3rd is for ads?How can i translate it
in webpage width?

Thanks