Cookies and Macs

I wrote a script that used cookies to track users (the cookie contains the user's ID#). However, there was a problem when it came to the Mac users, the cookie that was assigned to them never stuck so every time they hit a page the script generated a new ID for them, made it very difficult to track them. Do Macs just handle cookies differently than PCs? What can I do to get a cookie to stick on a Mac so I can pull the data from it later? Thanks in advance! - Joshua Chapman webmaster of faxonautolit.com