I personally find the debian packaging system unfriendly so I don't touch it. Instead I have just compiled openmsx myself and copied all relevant files over to my phone. I can of course provide you with a tar ball which you can extract at the root of the file system and everything should fall nicely in place. Now if someone would be interested in writing a Qt based version of catapult or such I'd be more than happy...
Manuel, if you plan on creating new packages, please make everything install under /opt in the device and perhaps just create a symlink to openmsx under /usr/bin. The space on the rootfs is rather limited but there's plenty of space under the fs mounted at /opt. If you plan on compiling openmsx yourself, ro, the easiest way is probably to get the maemo sdk vmware image and do it inside the virtual machine. Then just copy the binary and data files to the phone with scp or by connecting your phone to your pc as a mass storage device.
jr, are you still alive?
If you look at http://talk.maemo.org/showthread.php?p=1189367#post1189367 you can see that 'ade' submitted a build to the official Maemo repository. Yay!
The bad news is that it's not the latest version, as ade had some real problems which I thought you had already fixed (all your patches are in the openMSX tree, so apparently something else is wrong)... The problems are: problems with the keyboard, performance (compared to 0.7.2/0.8.0, might be due to reverse not being disabled or horizontal_stretch not being disabled?), and with 0.8.2 there are problems in the video (garbled video).
jr, can you please help out??
Still breathing. Nice, I hadn't noticed the launcher, probably because I'm not using my N900 much these days.
I could try to test it out if I find my phone (and investigate if I get a working compilation environment in place again). FWIW I had openMSX compiled for the N9/N950 last year and it was working fine.
If I remember correctly in order to get full rendering speed the application needs to run in fullscreen mode. If there are any 'standard' UI controls visible like buttons or menu bar you get lousy performance because the graphics goes through composition in the window manager.