Net-SNMP is provided in Solaris 10 release now, and how to use it is descripted in this article.

To disable Sun's SNMP
#svcadm disable svc:/application/management/snmpdx:default

the Net-SNMP daemon program locates at /usr/sfw/sbin/snmpd, and configure file of snmpd saved with the name snmpd.conf at /etc/sma/snmp. Use svcadm to start of stop snmpd:
#svcadm enable svc:/application/management/sma:default
#svcadm disable svc:/application/management/sma:default

Log File
if there's any error or warning messages, see the file /var/svc/log/application-management-sma\:default.log. The default log file of snmpd is /var/log/snmpd.log.

Configuration file
We may use /etc/sma/snmp/snmpd.conf.save as the working configure file to test wheather our snmpd daemon is ok.
#cp /etc/sma/snmp/snmpd.conf.save /etc/sma/snmp/snmpd.conf
#svcadm restart sma

P.S. There's another file also named as snmpd.conf stored in /var/sma_snmp directory, and which is called persistent storage file. The persistent storage file, /var/sma_snmp/snmpd.conf, contains USM security information and any MIB components that are set for persistent storage. This file also contains the engineID and the engineID boots. This persistent storage file is automatically updated when the System Management Agent starts. When the System Management Agent stops, the snmpusm and snmpvacm utilities write user security information to this storage file.

Using the AgentX Protocol
The AgentX protocol is supported in the System Management Agent. By default, the System Management Agent ships with a secure profile, that is, read–only access. AgentX allows interaction with third party subagents, provided that these subagents support AgentX over Unix Domain Sockets. For security reasons, AgentX is not supported over TCP/UDP. For more information on the AgentX protocol, see http://www.ietf.org/rfc/rfc2741.txt Edit the main /etc/sma/snmp/snmpd.conf configuration file to configure the System Management Agent to use the AgentX protocol. By default, the AgentX protocol is disabled. The following procedure describes how to enable the AgentX protocol. To enable the AgentX protocol add the following to /etc/sma/snmp/snmpd.conf file:

master agentx

restart the sma (system management agent).
# svcadm restart svc:/application/management/sma:default

Using the SMA
To view the status of the agent
# svcs svc:/application/management/sma:default

To See Which MIBs Are Initialized
# /usr/sfw/sbin/snmpd -Dregister_mib -Dmib_init -L

To Check the Disk Space and Network on a Local or Remote Machine
# /usr/sfw/bin/snmpwalk -v1 -c public localhost HOST-RESOURCES-MIB::hrStorageIndex

# /usr/sfw/bin/snmpget -v1 -c public localhost HOST-RESOURCES-MIB::hrStorageSize.1

# /usr/sfw/bin/snmpwalk -v1 -c public localhost HOST-RESOURCES-MIB::hrStorageUsed

# /usr/sfw/bin/snmpnetstat -v 2c -c public -a localhost

if all these works, congratulations, the sma is configured and brought on properly.