With PPPoA (Point to Point Protocol over ATM) you need to to terminate the PPPoA link on a device with an ATM interface. You might be able to bridge the PPPoA interface on the modem with one of the LAN interfaces and connect that to the OpenWrt router.
However in the UK a lot of ISPs will accept both PPPoA or PPPoE automatically dependent on what your gateway wants to use. In that combination you still need the modem to bridge the ATM or VDSL interface with an ethernet interface but it will be possible to terminate the PPPoE link on the OPenWrt router....
As I said PPPoA requires an ATM interface, since WRT32x lacks such an interface there is no use in compiling the modules...
I reset everything and tried again and it's worked, I didn't put in any VLAN settings before because I didn't know what they should be but I tried what you've got in your screenshot this time. Thanks very much!