Custom Block Code to Count Members in Certain Usergroups

[Ranger375]

I basically want to create a block in my side bar that will display a total number of users total in my X, Y, and Z primary user groups. So basically it will ultimately say something like "To date, this site has 124 vetted members" and the bold number would change as members are moved in or out of the select groups. Does anyone know how to make this possible?

Thanks !