Just installed that latest 0.6.1 on a CentOS 5.4 x64 server. I as able to add the first site during the install, but no matter what I do, trying multiple browsers (FF, Chrome, EI etc) I am unable to add any more web sites? I found some other users with this issues but their suggestion (clear cache) had no effect.
To add a new site (or change existing site settings like currency and time zone) you have to klick on the green check button on the outer right of the table (not the save button at the bottom of the page)
If there’s no green check button, maybe this could help: