I stand corrected. There just too many people out there that get XHTML, PHP and CSS mixed up because they don't know what does what. Since the WordPress tags aren't really PHP (although they are driven by PHP) one usually doesn't get into the whole classes and functions level of PHP when designing themes or template files.
You would have to do that with PHP probably with a hack (I'm not good with PHP). CSS3 will provide the possibility to create columns but I take it you don't want to wait till it's supported by all browsers. Who knows someday when Internet Explorer 15 is released it might support CSS3.
Maybe you could try creating two list one with the odd post ID numbers and one with the even post ID numbers, although that might not give you the order you'd like.