Following my previous comment, I seem to have solved the problem. Here are the major steps (the impatient can find a summary at the end of my comment):

0. My system
SUSE 10.0, kernel 2.6.13-15.8-default, ALSA 1.0.9b

1. Sound Configuration.
The sound configuration of WINE has been changed by wine HQ and is now (versions after July 2005) only possible through the registry (the ~/.wine/config file is happily ignored by the new versions). The best way to configure your wine sound system is to do

# for cxoffice
$ wine --wl-app winecfg

or

# for the "regular" wine
$ winecfg


When you issue this command from the shell, the configuration window pops up. Select the Audio tab, and choose ALSA. (Sometimes I had to choose something else first and then ALSA to force the program to take over the selected parameter).

2. Midi driver setup in BIAB.
Now I can do (from the Band-In-A-Box wine-directory)

$ wine bbw.exe


and do "Opt." -> "Midi driver setup" and (WOW!) I can see my MIDI devices.
I don't have a MIDI-"enabled" sound card, so I need to play either through the MIDI-piano, or use timidity. However, using timidity is a little tricky:

3. Timidity.
The version of timidity I have (2.13.2-52) does not communicate correctly with Band-In-A-Box. It does receive MIDI data, but in a wrong way. I verified this by patching timidity from the source code (playmidi.c) to give me the MIDI events it acutally receives. The channels are screwed up. The reason is some weird combination of how Band-In-A-Box sends the MIDI events, ALSA, and timidity. (I tried Sweet-Midi, a Windows midi-player, and it worked fine with timidity). When I dump the midi events BIAB sends using

$ amidi -p virtual -d &

(and using the "virtual" MIDI-device in BIAB), the events from BIAB seem o.k. But how to get marvellous timidity back in business?

The good news: I found a work-around using Midi-Through. I need to start timidity as usual, e.g.,


$ timidity -iA -B2,8 -Os &
Requested buffer size 2048, fragment size 1024
ALSA pcm 'default' set buffer size 65536, period size 16384 bytes
TiMidity starting in ALSA server mode
Opening sequencer port: 128:0 128:1 128:2 128:3


And then do

$ aconnect 62:0 128:0


The magic 62:0 and 128:0 happen to be the port my Midi-Through virtual sound card is using and the port timidity offered when you started it. You can find out what you have to use instead of 62:0 by typing

$ cat /proc/asound/devices


and look for "raw midi" in the output.

Now, restart BIAB, goto Opt.->Midi driver setup, select Midi-Through, and try to play something. You shoud get timidity sound!

A final remark: I tried Midi-Through also to get BIAB sending its events to a VST-plugin using FST (Native Instruments Akoustic Piano). There I needed to disable "Midi-Thru" in the Midi driver setup window. Otherwise, even a single Midi event seemed to bounce back and forth between BIAB and the VST, finally forcing the VST to die of Midi event suffocation.

4. TODO
I have not had time to test any latency issues when playing a "real keyboard" throug BIAB related to this setup. Anyone interested, drop me a line.

5. SUMMARY
Here is a summary of the whole setup:

# -- Configure wine to use ALSA
$ winecfg # for "regular" wine
# -- for cxoffice # for cxoffice wine
$ wine --wl-app winecfg