Linux Total CPU idle
% snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.2021.11.11.0
% snmpwalk -v 2c -c public localhost ssCpuIdle.0

Linux Total CPU Usage
% snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.2021.11.11.0 | awk '{print 100-$4}'
% snmpwalk -v 2c -c public localhost ssCpuIdle.0 | awk '{print 100-$4}'

Linux Total CPU Usage For mrtg target
% snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.2021.11.11.0 | awk '{print 100-$4 "\n" 100-$4}'  

Invididual CPU Usage (Windows 2003, Linux)
% snmpwalk -v 2c -c public localhost 1.3.6.1.2.1.25.3.3.1.2
% snmpwalk -v 2c -c public localhost hrProcessorLoad

Total CPU Usage (Windows 2003, Linux)
% snmpwalk -v 2c -c public localhost 1.3.6.1.2.1.25.3.3.1.2 | awk 'BEGIN {sum = 0;}; {sum += $4} ; END {printf("%d", sum/4)}'

Total CPU Usage For mrtg target (Windows 2003, Linux)
% snmpwalk -v 2c -c public localhost 1.3.6.1.2.1.25.3.3.1.2 | awk 'BEGIN {sum = 0;}; {sum += $4} ; END {printf("%d\n%d\n", sum/4, sum/4)}'

Get all mib value
% snmpwalk -v 2c -c public localhost > FILENAME.txt

Get all mib
% snmpwalk -v 2c -c public localhost > all_mib.txt

View all_mib.txt and find to need mib value

Example
In all_mib.txt FILE
HOST-RESOURCES-MIB::hrProcessorLoad.768 = INTEGER: 1

% snmpwalk -v 2c -c public localhost hrProcessorLoad.768

Total CPU idle in Linux (Using net-snmp)
% snmpwalk -v 2c -c public localhost 1.3.6.1.4.1.2021.11.11.0