Mobile and HTML

Since yesterday I have been putting content into a mobile site for a company via a cns system that Pixillion had set up.  Pretty simple, just take the text in the word doc and put it into the html form so that it will look the same when run.  One annoy thing though, it seems in XHTML Mobile 1.0 the sub html tag does not work so all the CO2's look a bit wrong.  Cant seem to find any info as to whether Im right or not.  Just been catching up on my psd splitting to html now as its something I havent attempted before but is vital for web design.  Seems pretty logical: use the splice tool to separate out all the images in the psd to separate files, build an html framework to fit the design and then pull the images in correctly both in html and css to create the final design.  Nothing I couldnt cope with there Im thinking.  My only dilemma is sizing in css, what with ems and pixels and percentages I dont quite see how people decide 1 from another.  Maybe it doesnt matter...