I tried boy install by Desktop Manager and install by visiting Opera Mini by Blackberry.
1. If you install by DM, it won’t work. Opera Mini 4.0 Beta can be found in the application list , but the desktop doesn’t show the icon.
So, remember visit the http://www.operamini.com/beta/
with the browser of Blackberry and then choose install.
2. there are two version, high memory version and low memory version. I tried the high one, it works. I guess the lower memory version works also.