Did you try the mibs in WUG MIB Library?

http://www.whatsupgold.com/support/mib-library.aspx

Yes I tried the mibs in the WUG MIB Library and they didn't seem to work. 

You are getting this error message because the default performance monitors are only looking at the OIDs in the HOST-RESOURCE MIB, and based on the error that you are recieving, those Nortel devices do not support that MIB.  You will need to create custom performance monitors for those devices.

Hi Montrey,

I believe I can help you out because I have just been playing around with these performance monitors for our Nortel switches. 

They use RAPID-CITY.MIB and you will need to create a customer performance monitor with this OID: 1.3.6.1.4.1.2272.1.1.20

If you use use SNMP Walk you should find some of the others like:
DRAM .1.3.6.1.4.1.2272.1.1.47.0
POWER SUPPLY .1.3.6.1.4.1.2272.1.4.8.1.1.2
TEMPERATURE 1.3.6.1.4.1.2272.1.100.1.2.0
See here for more OID's: http://www.oidview.com/mibs/2272/RAPID-CITY.html

This will depend on the switch that you query as some of these may not have these OID's populated.

Thanks Michael.  I will able to get the CPU performance monitor for the Nortel PP1624G.  I am still searching the Mibs to see which one works with the Nortel 4550, 425, and 5500 switches

For my 5500's running v6.2.4 I found all the CPU information in this OID:
1.3.6.1.4.1.45.1.6.3.8.1.1

If you walk this OID you will see the options for last 10s, 1min etc for each of the units.

Here are the temp OID's:
1.3.6.1.4.1.45.1.6.3.7.1.1

If you need more info, Google nortel 5500 cpu oid

We have a 5510-48T v5.1.2  the OID is
1.3.6.1.4.1.45.3.53.1   

4550T-PWR v5.2.2.013 the OID is
1.3.6.1.4.1.45.3.71.4

425-48T v.3.6.1 the OID is
1.3.6.1.1.45.3.57.1 

These look like they should be in the Synoptics-Root-MIB but they're not in the one on OIDview site.  Does anyone know where I can find correct mibs for these 3 devices? 

@Montrey - Are the RAPID-CITY MIBs not working for you?

@Jason - The RAPID-CITY MIBS worked for the Nortel PP1624G device but the 5510, 4550T, and 425 looks like they use the Synoptics MIBs because I googled the OID and they are suppose to be under Synoptics-Root-MIB .

http://www.snmplink.org/cgi-bin/nd/m/Ent/N/Nortel%20Networks/![ALL]/ERS4500%20-%20Ethernet%20Routing%20Switch%204500%20Series/*25v5.0.0.003/SYNOPTICS-ROOT-MIB.mib

I have searched around and haven't been able to come up with anything.  Do you have a support contract with Nortel?  I would recommend giving them a call.