Check out the link that Tunix provided. It looks like a pretty good tutorial. After you attempt that post if you are still having problems. If IIS running FTP is similar to running it in Windows Server 2003 - then you will have to create multiple accounts for your friends to log in, and then set permissions for the users or group.
If you think that tutorial is to much then you may want to use another program to run your ftp. You can look at filezilla - which if I remember was very simple to get setup.
FileZilla - Server Download
Let us know which you are using and what problems you are having.