Cacti doesn't find my localhost interfaces

[rgriffiths]

Trying to graph traffic on my Raspberry Pi interfaces, Eth0, and WLAN.
executing ..
sudo snmpwalk -Os -c cacti -v 1 localhost .1.3.6.1.2.1.2.1.0
returns ..
ifNumber.0 = INTEGER: 3

but my cacti setup panel debug shows .. (NO Interfaces found)
+ Running data query [1].
+ Found type = '3' [SNMP Query].
+ Found data query XML file at '/var/www/html/cacti/resource/snmp_queries/interface.xml'
+ XML file parsed ok.
+ Executing SNMP get for num of indexes @ '.1.3.6.1.2.1.2.1.0' Index Count: U
+ Executing SNMP walk for list of indexes @ '.1.3.6.1.2.1.2.2.1.1' Index Count: 0
+ No SNMP data returned

Memory and Processes statistic graphs are working, but CPU Load and Logged-in Users remain blank
So I assume snmp and cacti are working together at least to be able to generate those 2 graphs.

Just can't work out how to get it graphing network traffic, which is what this project is all about .. monitoring the traffic thru our office 24-port managed switch.
We have been using MRTG on a standalone Fedora 16 server up to now, and I'm trying to transition to Raspberry Pi/Cacti.

Three days with doco and tests .. can't figger it out

Any help/advice appreciated.

Russell