All of our IOS and CatOS SNMP agents are multi-lingual. That is, if you configure an SNMP community string in IOS or CatOS, that string can be used for both SNMPv1 and SNMPv2c. For IOS, you configure a community string with:
snmp-server community MY_STRING ACCESS
Where MY_STRING is your SNMP community string and ACCESS is one of "RO" for read-only access or "RW" for read-write access. For CatOS, you configure a community string with:
set snmp community ACCESS MY_STRING
PIX/ASA is different. The PIX and ASA only support SNMPv1 (and in later version of code SNMPv3). The PIX will not do SNMPv2c.