Site looks broken in mac. why?

I created this site for a friend:

I don’t own a mac, but when viewed on a mac I am told the tables appear broken and its not all nice as it is on a pc. No page is really that viewable on a mac. Why is that? I know there may be some font css issues between mac and pc, and I might have to change my css code to accomodate a mac, but why the table tags appearing broken, choppy? I used the usual TD, TR, etc. Any help would be appreciated.