For future reference you should show the things that you have tried. We aren't a code-writing service.

That being said you should look at Date::Simple. What you want to do is find the first thursday of a year. Date::Simple uses Sunday as the 0th day of the week so Thurs is the 4th. I used Date::Calc because it was on my computer already.

use Date::Calc qw(:all);
$count = 0;
#insert your own year.
$year = "2011";

#set $date to the first day of the year
@date = ($year,1,1);
print Date_to_Text(@date) . "\n";
#find the next thursday
if(Day_of_Week(@date) > 4)
{
    @date= Add_Delta_Days(@date,7-Day_of_Week(@date)+4);
}
else
{
    @date=Add_Delta_Days(@date,4-Day_of_Week(@date));
}
#now you have the first thursday.  Now just count how many
#until you reach a new year
while(@date[0] eq $year)
{
    $count++;
    @date=Add_Delta_Days(@date,7);
}
print "$count thursdays in $year\n";
[download]

You should probably verify that the results are correct. They seem to make sense to me but that doesn't mean much. Hope this helps.