simple date question

this is pretty simple but my brain's not working I get the numerical value of a week in the year thus e.g $today = date("W"); gives 4 .so this is the 4th week of the year. I want to get the month based on this number. e.g 4 should be january. 7 will be feb etc.. i'm not bothered about being too exact ,where some weeks are in 2 separate months, the earlier month should be displayed.and this is just for 2003. thanks, adrian