Real,
I have Windows RT 8.1 and I don't see anything in the VPN connection properties indicating "full" support for IPSec groupname+password authentication, which is essentially what most companies using Cisco VPN seem to utilize. I could be wrong and I even hope I'm wrong, but I don't think so.
This link is frequently referenced:
http://technet.microsoft.com/en-us/library/jj900206.aspx
...but the only IPSec authentication supported is still through a certificate or pre-shared key.
Feel free to post a screenshot of the appropriate Win RT 8.1 dialog to prove me wrong. Please prove me wrong.