http://office.vtc365.com/twiki/bin/view/Main/WebRss
For other TWiki webs, replace /Main/
with the name of the web:
http://office.vtc365.com/twiki/bin/view/Public/WebRss
http://office.vtc365.com/twiki/bin/view/Sandbox/WebRss
http://office.vtc365.com/twiki/bin/view/TWiki/WebRss