How did you start microemulator?
Do you have the latest jar file of Opera Mini?
Go to http://www.opera.com/mobile/download/versions/ select your Opera Mini version, hitw View Downloalink, download opera-mini-latest-advanced-en.jad and opera-mini-latest-advanced-en.jar.
May be you will use http://mini.opera.com/download-7/opera-mini-latest-advanced-en.jad?no_redir&ismobile=false and http://mini.opera.com/download-7/opera-mini-latest-advanced-en.jar?no_redir&ismobile=false for latest Opera Mini 8.
On my emu only 7.1 worked.
Did you store the opera-mini-7.1.32052-advanced-en.jar and ...jad (or newer) into microemulator's subfolder /apps?
In Shell with java -jar microemulator.jar
After start of micromeulator select File -> Open Midlet file
Select opera-mini-7.1.32052-advanced-en.jar
Select Start in Opera Mini emulated phone
Opera Mini should start now