taborious--please look at the previous link--it shows with an example, the correct OID to get the amount of memory available to a processor.
Something that probably needs explaining, when you state "There are a certain set of MIBs loaded by default", this statement is true, however you can not come back later and load additional MIBs in the device. If you want additional Mibs or OIDs, you will need to upgrade IOS to support the additional MIBs you're looking for.
Having said that (and probably not very clearly), have you performed an "snmpwalk" on the devices? Doing so may give you the information you need.
There's probably a way to do this in windows, but for *nix boxes, try this:
"snmpwalk -c snmp-ro -v 1 device-ip > somefile"
Scroll through the "somefile" and look for the OID(s) you want to graph. You can also add other switches such as "enterprises" or "ISO" after the device-ip to get specific parts of the OID tree.
Keep in mind, some things simply don't have a MIB or OID associated with them, you will have collect the appropriate MIBs and do some type of math or manipulation to get what your looking for. For instance, if there is no "Total DRAM" mib, but there are "DRAM used" and "DRAM Free" MIBs available, simply adding these two values together would give you the total amount of DRAM available.
hth
