Getting information about DHCP using SNMP

Hello all,

I'm having a bear of a time getting information about a DHCP scope using
SNMP. It seems pretty straightforward so I'm wondering where I've gone
wrong. Here's what I've done so far.

On the server that hosts the DHCP server, I've installed the SNMP agent from
'Add/Remove...' in Control Panel. I've setup the service with a RO community
string of 'public' and I've configured the service to allow queries from the
localhost (since I'm running the SNMP toolset from this same server, that's
all I should need). I know that the SNMP agent is working because I can get
information from the agent about the server using OID strings such as
1.3.6.1.2.1.1.3.0 (which returns the server uptime). I can even get
information from the agent about the DHCP server using OID
1.3.6.1.4.1.331.1.3.1.1.0 (which returns the DHCP Server startup time).
However, I can't seem to figure out the correct OID for getting information
about the DHCP scope. For instance, I'd like to get the number of addresses
available in the lease pool so that I can send out an alert if it drops below
a certain value. By my estimation, the OID string should be
1.3.6.1.4.1.331.1.3.2.1.1.3, but that doesn't produce anything. Any help
would be appreciated. Thanks.

Steven