Displaying number of posts each month in archive

Hi,

I recently downloaded a theme for my site, but in the archives in my sidebar, it displays each month you can click on, but it doesn’t show the number of posts made that month (eg. it displays May 2010, but I want it to display May 2010 (xx), where xx is the number of posts that month.) Does anybody know how to go about fixing this? I couldn’t seem to find an exact answer while searching.

Thanks.