If you are trying to import mibs with dependencies on other mibs you will have to set the MIBDIRS environment variable.
Unix / Linux: export MIBDIRS=/home/<user>/MIBS:/usr/share/snmp/mibs
Window: Good luck! No really. Try this url out. It has everything that you need to know about setting environment vars in windows.
http://vlaurie.com/computers2/Articles/environment.htm