Firstly, I'm no super expert. So my knowledge might be patchy in places. The following has been gained from trying things and eventually getting them working...

I can't remember the exact procedure but have a look through these fora and you will find the info to run the latest JVM from Oracle (more recent than icedtea).

Roughly speaking, there are 3 types of java programmes: stand alone for SE, stand alone for ME and web run-time.

The N900 can run the desktop version (SE) of the JVM, compiled for armv7 devices. Therefore java programmes can be run from the command line, once device is prepared. To run frequently used software, associate an icon with the line or two of shell that will init your programme. NB. IcedTea is for running stand alone (offline) software; it does not run web based java programmes, certainly without a lot of tweaking!

I really thought there was a Java web runtime included in microB, unless there's a version mismatch? Check the Wiki for this. Perhaps you need to do something in the browser's about:config to enable it?

There is also a reasonably recent (Spring/Summer 2011) micro emulator for software that runs in ME mode. Have a look through previous threads for this. This ME runs stuff normally designed for other devices like Symbian, Android etc. It's not quick but it can be useful.

Edit:
This has some good information
http://www.oracle.com/technetwork/ja...ech/index.html
Probably, you want to set up the webstart feature for the browser. Bit of a faff is sorting out Java but very useful if you need its capabilities!

The alternative is to use the browser in EasyDebian. It has all this sort of stuff preconfigured.