This works:
IF-MIB::ifInOctets["index","IF-MIB::ifDescr","eth0.4"]

But this doesn't work:
IF-MIB::ifInOctets["index","IF-MIB::ifPhysAddress","0:d0:cf:6:3:77"]

1433:20091223:183623.215 Item [10.1.1.1:IF-MIB::ifInOctets["index","ifPhysAddress","0:d0:cf:6:3:77"]] error: Cannot find index [IF-MIB::ifPhysAddress] of the OID [IF-MIB::ifInOctets["index","IF-MIB::ifPhysAddress","0:d0:cf:6:3:77"]]: NOT FOUND: IF-MIB::ifPhysAddress[0:d0:cf:6:3:77]

[root@backup ~]# snmpwalk -v 2c -c aaa 10.1.1.1 IF-MIB::ifInOctets
IF-MIB::ifInOctets.1 = Counter32: 259247
IF-MIB::ifInOctets.2 = Counter32: 0
IF-MIB::ifInOctets.3 = Counter32: 0
IF-MIB::ifInOctets.4 = Counter32: 0
IF-MIB::ifInOctets.5 = Counter32: 0
IF-MIB::ifInOctets.6 = Counter32: 2489979454
IF-MIB::ifInOctets.7 = Counter32: 2557924516
IF-MIB::ifInOctets.8 = Counter32: 0
IF-MIB::ifInOctets.9 = Counter32: 0
IF-MIB::ifInOctets.10 = Counter32: 0
IF-MIB::ifInOctets.11 = Counter32: 3889132176
IF-MIB::ifInOctets.12 = Counter32: 18118273
IF-MIB::ifInOctets.13 = Counter32: 1768038893
IF-MIB::ifInOctets.14 = Counter32: 2109895140

[root@backup ~]# snmpwalk -v 2c -c aaa 10.1.1.1 IF-MIB::ifPhysAddress
IF-MIB::ifPhysAddress.1 = STRING:
IF-MIB::ifPhysAddress.2 = STRING:
IF-MIB::ifPhysAddress.3 = STRING:
IF-MIB::ifPhysAddress.4 = STRING:
IF-MIB::ifPhysAddress.5 = STRING:
IF-MIB::ifPhysAddress.6 = STRING: 0:d0:cf:6:3:73
IF-MIB::ifPhysAddress.7 = STRING: 0:d0:cf:6:3:74
IF-MIB::ifPhysAddress.8 = STRING:
IF-MIB::ifPhysAddress.9 = STRING:
IF-MIB::ifPhysAddress.10 = STRING:
IF-MIB::ifPhysAddress.11 = STRING: 0:d0:cf:6:3:73
IF-MIB::ifPhysAddress.12 = STRING: 0:d0:cf:6:3:77
IF-MIB::ifPhysAddress.13 = STRING: 0:d0:cf:6:3:75
IF-MIB::ifPhysAddress.14 = STRING: 0:d0:cf:6:3:76

[root@backup ~]# snmpwalk -v 2c -c aaa -O0 10.1.1.1 IF-MIB::ifDescr
IF-MIB::ifDescr.1 = STRING: lo
IF-MIB::ifDescr.2 = STRING: teql0
IF-MIB::ifDescr.3 = STRING: tunl0
IF-MIB::ifDescr.4 = STRING: gre0
IF-MIB::ifDescr.5 = STRING: sit0
IF-MIB::ifDescr.6 = STRING: eth0
IF-MIB::ifDescr.7 = STRING: eth1
IF-MIB::ifDescr.8 = STRING: ipsec0
IF-MIB::ifDescr.9 = STRING: ipsec1
IF-MIB::ifDescr.10 = STRING: mast0
IF-MIB::ifDescr.11 = STRING: eth0.1
IF-MIB::ifDescr.12 = STRING: eth0.4
IF-MIB::ifDescr.13 = STRING: eth0.2
IF-MIB::ifDescr.14 = STRING: eth0.3