This information is available on cco in the url below
and I have also included a snip of the minimum requirements.
http://www.google.com/search?q=cache:8qoanq4cXGE:www.aarnet.edu.au/projects/voice/billing/Cisco1999TedHuff.pdf+configuring+aaa+h323+voip+radius++cisco&hl=en
!
aaa new-model
aaa authentication login default none
aaa authentication login h323 radius
aaa accounting connection h323 start-stop radius
!
radius-server host 10.1.11.11 auth-port 1645 acct-port 1646
radius-server key testing123
!
gw-accounting h323