The PIX only uses SNMP v1. From the 6.3 docs:
"Use CiscoWorks for Windows or any other SNMP V1, MIB-II compliant browser to receive SNMP traps and browse an MIB. SNMP traps occur at UDP port 162"
In order to get the hits for an acess-list entry, you can type 'show access-list'. This will give you the number of hits on each entry of the access-list. Remember that a hit will only occur for packets that do not have an existing connection, i.e. packets for new connections will be the only packets that will register on the hit counter.
Hope this helps...
Marcus