To find out which version you are running just go to Site Management under your site database. RTM is 4.00.5931.0000 and SP1 is 4.00.6221.1000.
Update 1: SP2 eval is 4.00.6468.2001
Update 2: SP2 retail is 4.00.6487.2000
To see if R2 is installed right-click and choose properties on the site, in this case 007 – System Center. On the general tab it will state if R2 is installed or not.